Ryosuke Kaihara

Prologue "Childhood" appearance. A university student living in Tokyo. A fanatical fan of Ai, to the point of being a stalker. The bottle of star sand that Ai had displayed at home was a gift from him as a fan.

Enraged by Ai's pregnancy, having somehow obtained the information, he pushed Ai's attending physician, Goro, off a cliff, killing him. Several years later, he again obtained information and this time stabbed Ai to death just after she had moved into a new home. His heinous act was driven by the belief that Ai wouldn't remember someone like him who had been supporting her, but even Ai, who was bad at remembering names, remembered Ryosuke's name and the gift he had given her. Shocked by this, he committed suicide.

According to Aqua's deduction, there was a mastermind who incited Ryosuke, the perpetrator, and it was from this person that he obtained information about Ai's hospital and new residence.