Ryosuke Kaihara

""You liar... To think you have a brat... Why... You deceived me...""

Ryosuke (リョースケ) was a pivotal antagonist in the Oshi no Ko manga series. He was an obsessive fan of Ai Hoshino whom he murdered after learning of her secret children before committing suicide to avoid arrest. Prior to this, he also killed Gorou Amemiya when the doctor interfered in his first attempt to kill Ai before she gave birth.

Personality
A shut-in, Ryosuke was a mentally unstable person who turned toward idols to feel loved in his life. As a result, upon learning that his top idol had "deceived" him by having children, he snapped and tried to kill her on two separate occasions, succeeding on the second.

Plot
After learning from someone that Ai Hoshino was pregnant, Ryosuke was enraged and went to the hospital where she was staying. Garnering suspicion from her doctor, Gorou Amemiya, a chase started between the two, ending with Ryosuke taking Gorou's life.

After a few years, Ryosuke would learn from the same person the address of Ai's new apartment. Concealing a knife within a bouquet of white roses, Ryosuke went to the apartment and fatally stabbed Ai in her home. As Ryosuke began to lash out at a bleeding Ai, she weakly told him that she wanted to love her fans, even remembering his name and the star sand he gifted her. Hearing those words caused Ryosuke to run away in horror and anguish, leaving Ai to die from her injuries.

Ai's death was announced to the public, and it was later revealed that Ryosuke had committed suicide shortly after. Because Ryosuke was already dead, the investigation revolving around Ai's murder ended instantly.

Trivia

 * It is theorized that the reason why Ryosuke committed suicide was to cover up for the same person who leaked Ai's address information to him.