Bokurano: Ours, Vol. 4 — Mohiro Kitoh

Having no interest in boys her own age, young Chizu develops a crush on her schoolteacher. After a few tentative secret dates, her relationship with the older man takes an unexpected and violent twist. When Chizu finally takes control of Zearth, she's got two things on her mind: save the planet and exact her revenge on her ex-lover.