Otona Riina

Shiina's younger sister. She lover her big sister and believes her sister is the best at everything. Since she saw Ryou on the first day of school, she always paying attention to him. She seems to be living a dream world where everything is always good, but only those close to her realize that she's not normal.

Spoiler

Because of the many years of sexual abuse and humiliation, she developed a fake personality that, although is similar to her original personality, for those close to her, is certainly not the same and overwrote her own memories of the day of the storm because of the trauma she suffered that day that day. However, even though she forgot about what happened that day, she still clearly remember Ryou and the fact that he saved them.

Future: She's not directly mentioned in the prologue's future, but it said that she's missing and might have suffered the same thing as her sister.