Kotomi Tsuda (津田 コトミ)

Takatoshi's younger sister, who is a third year in junior high school and plans to attend Ōsai like her brother. She is considerate and caring toward others, but is curious and enthusiastic about adult matters, to the point of frequently behaving similarly to Shino Amakusa (to the point that both brought Takatoshi adult manga when he was sick).