Bokura ni Namae o Tsukeru Nara

Reunited after seven years following their parents' divorce, high school senior Izumi Tohsaka must now share a dorm room with his younger brother Kaoru Yano. But this isn't the kid he remembers—Kaoru has dyed red hair, a deep voice, and carries a different surname. Izumi finds himself drawn to this mysterious, mature stranger who feels both familiar and completely new.