Ryosuke Kaihara

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

- Ryosuke to Ai Hoshino

Ryosuke Kaihara was a pivotal antagonist in the Oshi no Ko manga series. He was an obsessive fan of Ai Hoshino, whom he murdered after learning that she had children, before committing suicide to avoid arrest. Prior to this, he also killed Gorou Amamiya when the doctor interfered in his attempt to kill Ai before she gave birth.

Appearance
Ryosuke has dark-brown hair and light-brown eyes.

Personality
A shut-in, Ryosuke was a mentally unstable person who turned toward idols to feel loved in his life. His room being filled with Ai's poster clearly shows his strong obsession on her. As a result, when he learned that his top idol had "deceived" him by having twin children, he snapped and tried to kill her on two separate occasions, succeeding on the second. However, when he was proven wrong about Ai not even remembering his name, regret may have instantly hit him, which he could not properly process, thus running away from the scene and committed suicide eventually.

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 Amamiya, a chase started between the two, ending with Ryosuke taking Gorou's life by pushing him off the cliff.

A few years later, 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 the stomach at 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.

In the upcoming movie 15-year Lie, Aqua, the sole witness to his crime, is set to portray him. The role then transferred to another actor, Tomo Ayabe.

Etymology

 * The name Ryosuke means "clear" (亮) (ryo) and "help, assist" (介) (suke).
 * Ryosuke's surname Kaihara means "shell/shellfish" (貝) (kai) and "field, plain" (原) (hara).

Trivia

 * Ryosuke's last name Kaihara is only revealed in Chapter 128 when an actor is casted as him for the movie 15 Year Lie.
 * It is theorized that the reason why Ryosuke committed suicide was to cover up for the same person who leaked Ai Hoshino's address information to him and presumably out of guilt because he found out that, unlike what he initially believed, Ai actually remembered him.