Rossweisse/Plots

Birth of the Breast Dragon Emperor
Rossweisse makes her first appearance in Volume 5 as Odin's bodyguard, reminding him of his status and telling him not to look at Serafall Leviathan lecherously. Odin responds by mocking her for not having a boyfriend, which caused her to break down in tears.

The Heroic Oppai Dragon
She later reappears in Volume 7 during Issei and Akeno's date, scolding them for being in the motel during the day and telling them that high-school students should stay at home and study. She then accompanies Odin to the Hyoudou Residence, scolding Odin for looking at Rias and Akeno's breasts lecherously before introducing herself to the Occult Research Club and was embarrassed when Odin added the point on her not having a boyfriend. She later helps in the battle against Loki and Fenrir and sealed Loki with her spells. She was abandoned shortly after that by Odin, much to her horror, claiming that she was fired. She was then persuaded by Rias into becoming her servant when she looked at the Gremory summary papers and is amazingly fascinated by the huge amount of money, premium insurance, and connection benefits she will receive by becoming a Devil under her peerage, and having a stable job of becoming a teacher at Kuoh Academy.

In Volume 9, she accompanies the second-year students to Kyoto. When Issei attempted to peek at the girls, Rossweisse attempted to stop him only to become another victim of Issei's Dress Break, much to her horror, due to the fact that her jersey (which was bought while on discount) was ruined. When Issei sees Azazel drinking in the morning and telling him that it is not good for his health, Rossweisse strongly agrees and lectures Azazel on the fact but was cut short after having being teased by Azazel on not having a boyfriend. Angered by that, she snatches his alcohol and drinks all of it, making herself drunk. This action, however, would indirectly cause her loss when she fought against Heracles.

In Volume 10, she and Koneko fought against Misteeta Sabnock and Gandoma Balam at the Rating Game between their masters, winning the match. She, Xenovia, and Yuuto Kiba would then face Sairaorg Bael but lost to the latter.

In Volume 11, Rossweisse goes back to Asgard to train after her defeat in Kyoto and in her match against Sairaorg but reminded Issei of his mid-term test and prepared a question paper for his reference before leaving.

In Volume 12, she returns after learning various defense magic from her homeland, which would allow her to defend against attacks that are 10 times more powerful than Heracles' Balance Breaker. She also told Rias and her comrades about the rumors that she heard in her homeland regarding the Vampires, that a certain noble Vampire house captured a Longinus possessor which lead to battles between Vampires. After Issei successfully passes his Middle-class Promotion test, Rossweisse like all the female members of the Occult Research Club, decided to go out on a date with Issei.

The Legend of Oppai Dragon and his Lively Companions
During the events of Volume 14, Rossweisse participated in the meeting of Mephisto Pheles in regards to making a pact with a Magician due to the Gremory group's recent popularity. Later, she participates in the meeting with the Vampires from the Carmilla Faction. She, along with the rest of the Gremory group (excluding Rias and Kiba), later team up with the Sitri group to rescue Ravel, Koneko, and Gasper after the three were taken captive by the Magician Faction.

In Volume 16, Rossweisse, along with the Occult Research Club members, Bennia, and Loup Garou, went to Romania to aid Rias and Yuuto, who were confined in the Tepes castle. On their way to the Tepes' castle, Rossweisse told Issei that she received an offer from Sona Sitri to become a teacher in the Rating Game school that the latter is building. She then participated in the attempt to stop the extraction of the Longinus, Sephiroth Graal, from Valerie Tepes and rescue her; fighting the enhanced Vampires and Grendel along the way. Rossweisse later teamed up with Yuuto to defeat the mass-produced Evil Dragons that were rampaging in the Tepes' castle town. After returning from Romania, she participated in the meeting for the formation of D×D.

In Volume 17, Rossweisse asks Issei to be her boyfriend, as she lied to her grandmother, Göndul, about having one. She later goes on a date with Issei under her grandmother's pressure. Heading to Tokyo, the date ends abruptly due to the sudden appearance of Euclid Lucifuge, who came to try and recruit Rossweisse into Qlippoth. Later on, Rossweisse joins the rest of the Occult Research Club and Student Council as they hold an open house for Sona Sitri's newly build Auros Academy, teaching many of the prospective students magic alongside her grandmother. At night Rossweisse entered the male's bathhouse where she meets up with Issei due to hot water being out in the female's, they have a discussion on her research on Trihexa, worried about being taken and used by the enemy, Rossweise asks Issei to kill her if it were to happen but he refuses to say he will protect her.

Unfortunately, Qlippoth suddenly attacks the school by putting up a huge barrier (also serving as a massive time dilation field where one hour inside becomes one minute outside) around the town and assaulting it with the mass-produced Evil Dragons army as well as Ladon, Azi Dahaka, Grendel, and Walburga. During the battle, Rossweisse served as a bodyguard for Asia, who was flying around the battlefield on Ryuuteimaru, Issei's familiar, to serve as a battlefield medic. At the climax of the battle, Euclid arrives and kidnaps Rossweisse, revealing that due to their loose resemblance, Euclid intends to turn Rossweisse into a replacement for Grayfia, as well as planning to tap into her knowledge of Trihexa's seals to further their goal of unsealing it. In the ensuing battle, Issei is able to overpower Euclid using his Wyverns and newly-acquired Longinus Smasher with Rossweisse using the magical rope Euclid tried to use on her to restrain him. In the end, Rossweise falls in love with Issei and ask him if they can go to a 200 yen shop next time.

Rossweisse and the Occult Research Club went to Heaven in Volume 18 to talk to Michael about the Christmas project the alliance is working on. After the meeting, Michael informed them about the deaths of Church officials and the presence of Evil Dragons found at the attacks. Rossweisse helped defend Heaven from the attack of Qlippoth. She, along with Rias, Koneko, Gasper, Yuuto, Akeno, and Cao Cao, fought against the group consisting of the Evil Dragon Ladon and three Grendel clones. She, Akeno, and Yuuto teamed up to defeat a Grendel clone and used the binding technique Euclid used on her in the Underworld to incapacitate another clone for Akeno to finish off. She is later seen along with the other girls observing the Interdimensional Room that Touji Shidou brought for Irina to be able to have sex with Issei without falling and commented on how her head was full of indecent thoughts and tried to expel them feeling it was too early for her.

In the Extra Life of DX.1, the Gremory Team participated in a rating Game rematch against Riser Phenex. Rossweisse teams up with Gasper and takes down three of Riser's Pawns, they waited at the replica of the main school building where they meet Issei and Asia being escorted by Mihae to her master, as Issei and Asia head to the roof, Rossweisse and Gasper face off against Mihae which the pair manage to win. The victory goes to the Gremory Team as Issei was able to defeat Riser.

In Volume 19, along with other members of D×D, Rossweisse took part in the battle against Church rebellions led by Vasco Strada and Ewald Cristaldi. After Vasco was defeated, Walburga and an army of Evil Dragons ambushed them, however, they gain the advantage when Rossweisse activated a barrier forcing the Dragon army to be immobilized, this action caused Walburga to activate her Balance Breaker that contained half the soul of Yamata no Orochi. however, Walburga was soon defeated and arrested. Along with her friends later heard the news about Ravel went missing during her brother and Diehauser's Rating Game.

In Volume 20, Rossweisse would help prepare students who are going through career consultation. D×D headed to meet with Ajuka who was able to recover Ravel but are told about the shocking truth about his secret creation; the King Pieces. When Issei's parents are kidnapped, D×D infiltrated Qlippoth's hideout on the stolen city Agreas to save them, Gasper uses his Balor form when the Gremory Team battle against the Evil Dragon who took Issei's family; Niðhöggr. All their attacks prove to be ineffective as the Dragon was equipped with several Pheonix Tears vials until Crom Cruach comes in and starts mercilessly beating Niðhöggr.

In Volume 21, when Issei was discharged from the hospital and met up with his friends, worried for his safety, Rossweisse gave him a Nordic talisman she made in the style of a Japanese charm amulet they head off into battle. During the war against Qlippoths army, Rossweisse had completed her 616 sealing spell and manages to cast it on the head of 666 and was able to seal the movement of the main bodies of the legendary beast. The spell, however, was unsuccessful in fully stopping 666 as the beast extract its core before it was fully sealed.

In Volume 22, one of their weekend off, the Occult Research Club, Vali's team and Issei's parents went on a fishing trip on an inhabited island owned by someone related to them. When Xenovia and Irina began a fishing competition, Rossweisse wore a wetsuit and attempted to catch fish by diving into the water with a harpoon.

Rossweisse and all of Issei's friends were present during his ceremony for graduating into a High-Class Devil. After the ceremony when Asia and Xenovia wanted to move to his peerage. When everyone's graduation ceremony had concluded, Rias requested that Rossweisse be also transferred, while Rossweisse was initially baffled by this, Rias hugged her and assured that she believed that Rossweisse will be able to release all of her potential the most by serving under Issei while in turn he will need her strength and support, which she accepted as the two shed tears. Immediately after, Rossweisse was among the ORC members present when Issei proposed to Rias.

Red Dragon Emperor of the Blazing Truth × White Dragon Emperor of the Morning Star: The True Dragon(s) of the Kuoh Academy
Issei's Team arrived fashionably late to the opening ceremony of the Azazel Cup while making a grand entrance by flying down with Ryuuteimaru. Ten days later, after going through the first few matches, their entire team receives bad ratings in the tournament. For their next match up, Rossweisse and her teammates would eventually go up against Baraqiel's team of Fallen Angels under the Rating Game rules Object. Rossweisse used her magic to locate and identify the object they needed to score points. The victor goes to her team when Issei defeated Baraqiel while proposing to Akeno.

In Volume 23, her team had just won another victory. In the waiting room, Rossweisse noted how one of the reasons for their continuing winning streak could be that they haven't faced any God-Class beings yet, for the rest of the time, they discussed how counter measures could be used against them no matter how strong they were. At school, an energetic Rossweisse stood upon the podium, now as the homeroom teacher of the third year’s B class, announced a ball tournament will be happening and that they cannot lose. After school, everyone continued their Devil jobs for a branch store of the Gremory Large Enterprise, Rossweisse's handled summon requests that required magic. She had just come back from a job with an antique clock that had been a decoration as appraisal, she handed it over to Ravel to check its worth with a professional. After Issei's talk with Asia, she and the other girls mistook it for some workplace romance.

Her team then had a meeting with their next opponents; Dulio and his team of Brave Saints at the Hyoudou Residence. Days later within the club room, the team had invited Ouryuu to increase their numbers. Once the matter had been settled, with two Student Council members on their side, Rossweisse felt it best to report back to the Gremory House that supports the school later.

When the time came for their match up against Dulio and his team of Reincarnated Angels, the game was set under the game rules of "Rampage Ball", in which both teams must find the goals that appear all over the game field and then throw the ball in. Before setting out, Rossweisse used her magic to improve everyone's physical abilities. The team then headed after the ball before the others did, they were met with thunderclouds created by Dulio that caused icy cold heavy rain accompanied by lightning strikes that they dodged. After a bit of a scuffle at first, their side had gained the first points. The game goes on for about two hours as both teams scored a roughly even number of points. Rossweisse supported Irina and Xenovia against Kiyotora Shinra and Dulio who had the ball and fired off large bursts of offensive magic at them, but Mirana-san created an extremely large spear of light to easily obliterate her spells. Rossweise was then forced to retreat when Griselda joined the fray with her bow and arrows and fired them at her. In the end, victory goes to Dulio's team with the score being 144 – 146.

When the school's ball tournament had commenced with the Occult Research Club playing Basket Ball against the Student Council, Rossweisse had motivated the ORC members that whether they win or lose, they shouldn't leave behind any regrets. The resulted scores ended in a tie.

In Volume DX.4, Rossweisse participated in the strategy meeting with her team for their upcoming match against Sona and her team. She and her team began to analyze the team members, She becomes surprise about Hoderi Yukihiko became a member of Sona’s team and heard that is part of his training for his advance to middle school. On the day of their match, Rossweisse and her team traveled to the Armaros Colosseum in the fallen angel’s territory in the Underworld and she noticed the teams were pitted against those with high offensive power and their win rate aren’t good. Under Ravel’s instruction, she was told to intrude the opposing team’s territory if there was opening and promote herself to queen to increase her characteristic as pawn, she later join together with Issei and Irina to Tsubasa and Ruruko‘s location to act as a supporter to the both of them. Rossweisse and Irina took on Tsubasa, while Issei deals with Ruruko and when he attempted to use dress break on her, she deflected his technique with her sacred gear and accidentally destroyed of Rossweisse’s and Irina’s clothes in the progress, much to their dismay. After Tsubasa and Ruruko were forced to retreat because of Grayfia destroying their recovery point, Rossweisse heads back to their team base with Issei and Irina, while also dressing in their spare clothes. Rossweisse and her team victorious due to Sona surrendering the match to them.

In Volume 24, when everyone came to the school pool for an enjoyable time, she watches on as all of Issei's fiancées fought over who should he apply suntan oil to first and claims that she should also get the right as his servant. They head back to the Hyoudou Residence when they hear that the parents and guardians of everyone else have arrived there, they learned the reason for their meeting was to discuss plans for wedding ceremonies for each of Issei's fiancées.

Soon, word came that Kuroka and Koneko were being targeted by Grim Reapers due to being involved in their late father's research in artificially creating Super Devils. When it came time for Rias and Vali's Rating Game match, Rossweisse used her magic to create a barrier over the stadium while every one of her comrades faced an army of Grim Reapers. In the midst of battle, Issei used the tail of his armor to wrap around Rossweisses chest to absorb enough energy for his new technique to use against Thanatos, the resulting effect cause her breasts to temporarily shrink.

Eventually when all their enemies were dealt with, Rossweisse and all her friends went to watch the ending of Rias' match, which they witnessed her having to reluctantly forfeit. Everyone then later payed Rias a visit at the medical room. She watches as almost all of Issei's fiancées requested kisses from Issei as Koneko and Kuroka were hogging him for themselves. A few days later, she and her team were gathered at their homes VIP room by Shemhazai to give them a certain item Azazel had handed to him, Rossweisse was given a Mistilteinn wand. They then met with the others who informed them of Mahabali's loss in the tournament and the opposing sides members; Verrine and Balberith whom they feel a tense pressure from as they claimed to be Super Devils. They began gathering information concerning the new enemies they've met earlier. Just then, Rossweisse received a message from her hometown saying that she'll partake in an arranged marriage with Vidar, news that cries out loud after a slow pause.

In Volume 25, Rossweisse was gathered with the rest of the team in Issei’s room and watched the rival teams achieving their victories. Rosswiesse wasn’t paying attention due to being lost in thought due to her marriage meeting with Vidar. At Kuoh Academy, Rossweisse was in charge of her class’s quiz but she had her mind elsewhere until the female student reminded her that the timer is over. The students started rumors about Rossweisse’s condition and began to spread around the school. As her grandmother Göndul arrives at the Japanese restaurant, Rossweisse argues with her about the marriage meeting with Göndul scolding her about not marrying someone as well raising a family and continued to scold Rossweisse for not allowing Issei to do perverted things to her.

The day of the marriage interview Rossweisse was accompanied by Göndul and Issei for her meeting with Vidar while also dressing formally in a yukata. While waiting in the Japanese-style room, Vidar arrived together with his maids Fulla, Hlin, Gná and they gave Rossweisse, Issei, Göndul a strict expression with Vidar reprimanded them asking to leave things to him. Rossweisse introduces to herself to Vidar as the former personal Valkyrie for Odin and currently a servant of Issei Hyoudou with Göndul and Issei also introduces themselves. Rossweisse and Vidar decided to talk about Odin and considers him a perverted old man that he went to go to all of the girl places and continued to have by bad-mouthing Odin. Rossweisse became astonished by Vidar remarking her as cute and accidentally drank all of Vidar’s beer and in a drunken state asked for five more beers. Rossweisse hugged Issei saying she will be Issei’s wife because he’s a promising Oppai Dragon and very kind to her as well the Underworld is more favorable compared Valhalla. Rossweisse began to cry and continued to say that Issei risked himself to save her from Euclid and became so happy. Rossweisse gets scolded by her senior Brynhildr who was also escorting Vidar for being weak towards alcohol and her intoxication disappears and continues to get scolding from her saying she she mistook Vidar’s beer as her own. Rossweisse and Issei gets shocked about Vidar declaring to get engaged with her and watched as Vidar challenges Issei with Rossweisse on the line.

After the interview, Rossweisse and her team started to analyze the members of Team Leisure of the Kings with her explaining Vidar’s abilities and his mystical boots is what puts him on par Thor. Watching her senior Brynhildr using magic, Rossweisse noted her activation is faster than hers with Grayfia pointing out the magic’s power output is the same and if their activation time and accuracy are better, they’ll lose by numbers. Rossweisse held her legendary weapon Misteltein wand in her hands and revealed to the team she still hasn’t mastered. Rias comes in and tells everyone that Ajuka is calling out to them at the VIP room who offered to help train them at the training ground and tell Ouryuu to bring them to Belzebut. During training in the Belzebut, Rossweisse was surprise by Ravel’s words that Issei is training hard for her sake and watches as the girls talk about Issei. Akeno asked Rosswiesse about her current feelings towards Issei after the interview and started to think about her feelings.

After returning from training at the Belzebut, Rossweisse wore a revealing lingerie and greeted Issei who also return from his training. She tells Issei that Rias and Akeno won’t be coming to the residence due to the things they had do in the Underworld and Asia will be sleeping with Xenovia and Irina. Rossweisse believes to reject the engagement she must offer herself to Issei and as she held his hand she revealed that she doesn’t want to marry Vidar and wants to be on Issei’s side. She ask Issei to snatch her away from Vidar and Issei responds to her that he never had any intention of handing her over to Vidar, recalling the incident he had with Euclid. Issei hugs Rossweisse asking to believe in her and Rossweisse gives him her first, much to Issei’s shocked. As they were kiss a second time, Kuroka burst into Issei’s room in order to do perverted things with him after learning that Rias wasn’t coming to the residence with Koneko soon following after her sister. Rossweisse gets surprise when Kuroka asked her if she wants to have Issei’s child and gets asked again by her but responded she will be sleeping with Issei which led the four of them sleeping together.

On the day of the match, Rossweisse and her team traveled to Valhalla in Norse mythology at the Thor Stadium. She gets many cheers from the spectators due to Valhalla being her home which causes her to blush from the cheers from everyone. As Team Leisure of the Kings arrives and the match starts Rossweisse goes together with Issei, Irina, Xenovia, Ravel, and Ouryuu to stairways of the artificial Yggdrasil. After Xenovia, Irina, and Ouryuu decided to take on the Chief-God of Olympus Apollon, Rossweisse place a barrier on them in order to keep them from out and she strengthens it with her Misteltein and placed another barrier on the cave where Grayfia and Asia takes on the Goddess Artemis. As they continued, Rossweisse and the others sees Typhon waiting for them at the one the floating islands and later sees Vidar inviting Issei to face him with Rossweisse and Ravel joining and leaving Typhon to Roygun, Bova, and Elmenhilde. While Issei fights Vidar on one on one, Rosswiesse takes on Brynhildr and her former colleagues alongside Ravel. Brynhildr asked Rossweisse if she been training as agrees she brought out her Misteltein as their fight starts. As Brynhildr and the Valkyrie Squad overwhelms Rossweisse with their combined attacks, Rossweisse reveals to them that she kissed Issei, much to their shocked and distraught. When the Valkyrie Squad released their attacking stance, Rossweisse and Ravel released their counterattack with magic and defeated the four Valkyries. In her final battle against Brynhildr, Rossweisse managed to defeat her by barrier magic just on Brynhildr's right foot and uses her Mistilteinn to enhance her offensive magic to defeat her senior. During the battle, Issei confessed to Rossweisse by asking her to give birth to his child and many children, which Rossweisse loudly agrees to give birth many of his children. Rossweisse and her wins the match due to Ddraig defeating Typhon and followed Issei to the top of the artificial Yggdrasil and held hands with him, shyly asking him to see real Yggdrasil to together with her and Issei agrees.

Rossweisse celebrates her victory at the Hyoudou Residence along with her team and the rivals teams. As the girls fight over Issei, she hugs him from his back and says that he is her husband and won’t hand him over in a drunken state after drinking alcohol again.

Rossweisse reappeared in True Volume 1, she gave her report to Issei about delivering the brochure by the company. After Rias made her announcement about her engagement with Issei to the Underworld and she suggested the girls should do a press conference, Rossweisse thought she should tell the Norse higher-ups since she was born a valkyrie. Rossweisse was one of the girls that was once contacted by Morisawa to be his girlfriend but she shyly revealed to already have a boyfriend which she revealed to be Issei, much to Morisawa’s displeasure. She joined the girls attempt to wash Issei’s body, with her washing his hair. After Issei was attacked by unknown devils, Rossweisse and the others arrived at the park to help transport the devils to the Underworld and she realized the devils that have been appearing in every mythologies and now Kuoh Town. After discussing about the devils, Rossweisse came to Issei’s room to sleep with him, but she’s fighting own temptation as it wasn’t her turn, but in the end she ended up sleeping with him with the other girls. Rossweisse and the others arrived at a town where the devils were residing and placed many powerful barriers so they can’t escape. After defeating the devils, Rossweisse and the others became surprise of seeing Issei, Ddraig, and Bova in pain because of a purple-haired girl singing, to stop her singing she cast a hypnosis magic on the girl. The group became astonished to learn from Ajuka that the girl is Ingvild Leviathan, a descendant of Leviathan and a half-human Longinus wielder. Rossweisse and the others took Ingvild to the beach of a unpopulated island so she can see the sea, with Rossweisse casting a barrier around the island until it was penetrated by the goddess Nyx.

After reporting Nyx’s actions to Ajuka and gained the approval from Apollon to defeat Nyx with condition of sealing her away, Rossweisse and the others headed to Nyx’s location. Rossweisse and Rias took on Nyx when Issei stepped out to use Akeno’s breasts to call Ingvild and her voice is heard through Rossweisse’s breast and the other girls. The girls breast began to glow as it powered up Issei and helps him defeat Nyx. After Nyx was defeated, Rossweisse headed to the Agares territory for the main stage of the tournament and learned they will be facing Rias and her team in the first match.

In True Volume 2, Rossweisse appeared in Issei’s dream of him being in his wedding ceremony, with Rossweisse among the first group of brides and tearfully, she shows her happiness. In the morning, Rossweisse went to do some training in the large training space on her own. After Ingvild returns from her first devil job with Issei, Rossweisse congratulated her and finds her payment cute as she thought it represents the White Dragon Emperor.