Sunny Ryoko (1987)

Kishimoto Kasumi, a 15-year-old girl, was supposed to live at her auntie's house in order to go to high school since April. However, when she moved to the house she was surprised with the fact that there were already four new male students living in the same house. To make the matter worse, that day while she was taking a bath, Takasugi Yusaku, one of those boys, came into the bath and saw her naked. This is how Kasumi's troublesome high school days started. (Source: AniDB)