Kuroka/Relationships

Issei Hyoudou
Their relationship seems to be initially hostile as their first encounter in Volume 5 when Kuroka tries to kidnap Koneko and as a member of Khaos Brigade. Kuroka attacks Issei and overwhelmed him, taunting Issei that he's much weaker than Vali. Later when Issei attained his Balance Breaker, he became more powerful that he can withstand her attacks, much to her surprise. While he stops before hitting her, planning to showing mercy, declaring that he will not stop next time if she tries to take Koneko.

She reappears in Volume 7, claiming Issei become more manly and asks him to have children with her because she is interested in the genes of the holders of the Sacred Gears of the Heavenly Dragons because they would make powerful offspring, but Koneko was challenging her that Issei was hers alone. The reason why she proposed Issei her offer because initially refused by Vali, so Issei thought that Vali was homosexual because no normal guy would refuse such an offer.

In Volume 11. When Koneko's in mating season, she attempts to seduce Issei after she managed to revert Koneko back to normal. Although this attempt is interrupted by an exhausted Koneko, declaring that Issei is hers. Kuroka leaves and quietly tells Issei to look after her sister, showing how much she cares for her sister. While recovering due to her injuries from Cao Cao, she explains to Issei the reason why she killed her master. Issei later lessens his hostility towards her, claiming she's clumsier than he is. Unamused by the conversation, claiming that she doesn't want to hear that from him, but later thanked him as he leaves seemingly without noticing.

In Volume 14 during her stay at the Hyoudou Residence, they became friendlier as Issei was willing to help the two sisters reconcile their relationship when the time comes, adding that Koneko's smile was the most important thing to him. Kuroka finally understood the reason why all the girls around Issei were falling for him, claiming that he was more charming than normal handsome men, providing evidence that she developed slight feelings for Issei.

In Volume 15, She became slightly closer to Issei, hugging him while rubbing her cheeks against his, telling him that he shouldn't become like the Evil Dragons and remains being the Oppai Dragon, and sitting on his lap.

Rias Gremory
Kuroka has been known to tease Rias with the nicknames that Bikou made up for her.

Koneko Toujou
She cares a great deal for her younger sister even though Koneko really hates her for what she did to their former master. Kuroka felt somewhat depressed and distant towards her sister for what she had done, even knowingly impossible for her to be forgiven.

During their reunion at the Young Devils Gathering, she plans on taking Koneko by force, even engulfing her in a fog of poison. She later admitted to Issei that she was happy at their reunion. She even put herself in harm's way when she was attacked by a reflected attck from Cao Cao as she wants nothing to happen to her younger sister and wants to protect her from everybody. She has put her trust in Issei to protect her since she has the potential to become a powerful and special member of her tribe. During the assault of the Grim Reapers, she jokingly ask Koneko if she want learn more about senjutsu and youjutsu from her, she later determinedly accepts.

Their relationship is somewhat improved as Issei stated that Koneko became a little happy during their training. She also planning on teaching her as an older sister efficiently, even reading extensive books regarding the basics of the energy flows within the body, senjutsu, touki, and such despite being an expert. Koneko became strict with Kuroka, telling her the reason she could stay in the Hyoudou Residence so she could train Koneko and Gasper.

Vali Lucifer
Kuroka tried to have Vali make love to her so she could have strong children but he refused her. Vali cares for her as a comrade as he was enraged when she was injured, especially when the injury was caused by his own technique (being reflected by Cao Cao). Kuroka also shows that she cares for Vali and respects him to a certain extent calling him "leader".

Le Fay Pendragon
Kuroka and Le Fay get along well being partners and are often shown working together. She even recommended Le Fay to be Issei's pact magician.

Bikou
Bikou and Kuroka constantly bicker with each other over the smallest issue when they are in some sort of troubled situation. Despite so, the two of them get along well because of their similar personality and stupidity.