Izumi-chan Graffiti(1980)

Kyouhei’s father has friends who will be working overseas for a while and has offered to let their daughter stay with them, which Kyouhei opposes. Kyouhei is a fairly typical tough teenager and doesn’t want to be shown as un-cool. Of course, Izumi, the girl who comes to live with them, rattles everything. She’s forward, doesn’t care about social standards and isn’t bothered by nudity – very much as modern a girl as Kyouhei is old-fashioned. But don’t count Kyouhei out; this is a doujo and he’s pretty good with that practice sword…

(Source: The Animeraider)