So: I'm in Primary School. What Now? (S01E01)

Fifteen-year-old Kaho Nikaidou steps out of her sheltered life and into a Tokyo high school dorm, only to have a shocking encounter with a truck! Just as things seem dire, a charming stranger swoops in to save her. Instantly smitten, Kaho tracks him down and bravely confesses her feelings. To her surprise, the dashing rescuer, Kanade, is actually the son of her new landlord! They start dating, but Kaho’s happiness quickly fades when she discovers that her new boyfriend is still in fifth grade!