Aika was Mahiro's sister that was brutally murdered. Her murder is the central mystery that haunts the narrative in the series. Aika had a penchant for quoting Shakespeare, particularly Hamlet and The Tempest by William Shakespeare.
[She secretly dated [Yoshino)(https://anilist.co/character/43737/Takigawa-Yoshino), whom she deeply loved. She stated that Yoshino is the only person she would date and that she would not consider anyone else, even if Yoshino were interested in another person. Mahiro is someone very important and special to her too, but not in a romantic way.]
