Riser Phenex

Riser Phenex is the third son of the Phenex Clan and the main antagonist of Volume 2 of the novels. He was once Rias Gremory's fiancé who has inherited the powers of the immortal bird, Phoenix, granting him immortality and instant regeneration. His all-female peerage consists of fourteen members.

Appearance
Riser is a tall and handsome young man in his early 20's with short blonde hair and dark blue eyes.

His outfit consists of a burgundy blazer with gold embroidery on the right with matching pants and black dress shoes. Underneath his open blazer is a white dress shirt that is not fully buttoned (just one button short), giving a slight view to his chest.

Personality
During his introductory volume, Riser is shown to be an arrogant, aggressive playboy with a holier-than-thou personality, tongue-kissing two of his girls just to agitate Issei and (in the anime) making improper advances on Rias. He is also condescending towards lower-class Devils, mocking Issei on his improper use of the Boosted Gear after the latter was defeated by Mira in one blow and labeling him as a weakling. Despite this, Riser does show an honorable side, as he allows Rias and her peerage ten days to prepare themselves for their Rating Game, knowing he would simply crush her and her peerage had she not accepted.

Later, after his defeat by the hands of Issei, Riser fell into a slump following his defeat, not moving out of his house after the loss. It is also explained that Riser developed a fear of Dragons as a result of losing to Issei and he became traumatized, upon seeing Issei and Dragons he would quake in fear. After recovering from his trauma, Riser seems to have reformed from his old ways, showing a degree of respect for his former combatants, especially Issei. For example, in Volume 10, he gives Rias advice on Rating Games prior to her match against Sairaorg, and in Volume 12, he gives his condolences to Ravel and Rias after Issei's supposed death.

History
Riser is the third (and youngest) son of the Phenex Family and the second-youngest sibling in the family, behind his sister Ravel. At some point before the start of the series, his family set up an arranged marriage between him and Rias (with her family's approval, as well) in an attempt to unite the two families and to preserve the bloodline of Pure-Blooded Devils.

The Red Dragon Emperor's Awakening
Riser made his first appearance in Volume 2 as Rias' fiancé. He came to the Occult Research Club, intending to take Rias back with him into the Underworld to get married with her which was refused by Rias. He then agrees to face Rias in a Rating Game under the condition if Riser wins, Rias has to marry him immediately while if Rias wins, their engagement will become invalid. During the Rating Game, Riser went to battle Rias while having his peerage deal with Rias' peerage. Riser manages to win his Rating Game against Rias after his Queen, Yubelluna, defeated all of her peerage except for Asia and Issei (the latter who has reached his body's limit), allowing Riser to beat Issei to near-death and forcing Rias to resign. During his engagement party with Rias in the Underworld, he faces Issei in a one-on-one fight with Rias' engagement on the line but loses due to Issei's strategy: namely using his new Dragon arm to splash Riser with a flask of boosted holy water.

Birth of the Breast Dragon Emperor
In Volume 5, Riser's sister, Ravel Phenex, revealed that Riser fell into a slump following his defeat by Issei, not moving out of his house after the loss. It is also explained that Riser developed a fear of Dragons following his loss.

The Heroic Oppai Dragon
In the side story "The Resurrected Immortal Bird", Issei asked Tannin to grab Riser against his will and take him to Tannin's territory that is full of Dragons in hopes of curing Riser of his Dragon Phobia. During his time there, Riser constantly complained and was pitted against a Blizzard Dragon which easily froze his flames much to his dismay. After finding out that the girls of the Gremory Team are going to the Hot Spring in Tannin's territory, Riser decides to go peep and battle against Issei who attempted to stop him from peeping which Riser lost after Issei used an underhanded move on Riser. Riser, however, was able to cure his Dragon Phobia.

Riser reappears in Volume 10, having recovered from his slump, giving some advice to Rias on the Rating Games and warning Issei that should he mistreat his sister, he will burn him to a crisp.

In Volume 12, Riser and his eldest brother, Ruval Phenex, went to the Gremory Palace to cheer up his sister and the Gremory Team before leaving with his brother to fight off the giant monsters created by Annihilation Maker.

The Legend of Oppai Dragon and his Lively Companions
Riser shows up near the end of Volume 14, hearing Ravel was in trouble and came rushing to help her only to find that it was all over.

In the Extra Life of DX.1, Riser is contacted by Ravel who tells him that Rias requests a Rating Game rematch which he agrees to. The Rating Game goes similar to their original match only with the Gremory team getting a better advantage, before the game, he had ordered Mihae to escort Issei to where he was so can get the chance to fight him one-on-one, Riser proclaims that he will continue to challenge Issei until he beats him no matter how long it takes. He was eventually defeated, making the victory go to the Gremory team

In Volume 19, Riser has a Rating Game with the Champion Diehauser Belial with Ravel having temporary rejoins his Peerage. When they finally face off, Diehauser had blocked their abilities with his "Worthless" and abducts them.

In Volume 20, Riser and his sister were finally recovered, he was sent home while stayed in Ajuka's care until the Occult Research Club could take her in.

Powers & Abilities
Immortality: As a member of the Phenex Clan, Riser shares his family's signature regeneration abilities, being able to regenerate lost limbs and recover from wounds instantaneously. However, his regeneration is entirely dependent by his level of Demonic energy. Being drenched in enhanced Holy Water caused high amounts of damage which stopped his regeneration altogether and he seemly couldn't heal damage that was inflicted on him by Issei while he was using a holy cross. His regeneration is also the cause of his arrogance, thinking it makes him immortal.

Pyrokinesis: Coming from a family that represents the Phoenix, Riser is capable of using fire based attack.

Flight: Being a Devil, Riser can fly using his fiery wings.

Hand to Hand Combat: In side volume DX1, it is mentioned that he trained Hand to Hand combat with Sairaorg Bael.

Trivia

 * Riser's height is 180 cm. (5 feet 11 inches) according to the visual book with his data, making him the fourth-tallest male character recorded in the series, behind Dohnaseek, Azazel, and Mil-tan.
 * Riser's Rating Game record (before defeating Rias) is 8 wins and 2 losses.
 * According to Rias, Riser lost those two games on purpose out of respect for one of the households his family was close to.
 * In the anime, Riser has a Greenwing Macaw parrot as a familiar.
 * A manga side-story reveals that Riser asked Ravel to be his Bishop so that he could have a full set of different "types" in his peerage, specifically the little sister and the tsundere.
 * In the Ophis side story "My First Errand", it is revealed that Riser likes hamburgers.
 * In the Funimation Dubbed version, Riser mostly refers to himself in the third person.