Boku wa Rounin Doutei Papa(1977)

Boku wa Rounin Doutei Papa

When Kotarou was riding a bus to the library, suddenly some kid called him 'papa.' Of course Kotarou was not interested at all. He just graduated from high school and was preparing to enter university after failing entrance tests several times. The kid still approached him and Kotarou fell for her. The kid name is Chitose and her mother is Kikko, a sixteen-years old.