Tongari Square Root(2003)

Tongari Square Root

Ruu is a high school student who studies seriously everyday, aiming to become like her genius brother, Shikyu. At this time, at Ruu's side, comes Jijyou, Shikyu's friend, who become's Ruu's teacher at home. Although Ruu's life has been messed up by the daring Jijyou, she has started to have feelings for him... (Source: Vampire Knights)