Yōichi Tanaka

Born on April 30th, blood type O.

He is Kou's older brother and the homeroom teacher of the advanced class. He is very worried about Kou, whose grades have dropped and who goes out alone at night. He thought Kou resented him for not being able to be there when their mother was sick.

He noticed that Kou liked Futaba because he saw Kou writing "Futaba Yoshioka" in his notebook when Kou was in middle school.

He was aware of Shuko's feelings and liked her too, but he rejected her confession because he feared losing control and the implications of their teacher-student relationship. Although he appears gentle, he is actually very thoughtful. He encourages Kominato to pursue Shuko.