Tenjiku Aoi

"Twin younger sister of Shion. Kind, innocent and child-like, but with strength of will. Dated Haru in university. Murdered by Shion, due to years of pent-up resentment and his fanatical devotion to Haru. Self-sacrificing and compassionate, she seems approachable, although her heart has walls that are hard to breach. Deeply admires her brother, with whom she shares a traumatic upbringing."
— A description of Aoi from the artbook.