Tonda Couple(1978)

Yusuke Tashiro moves to Tokyo to attend Hojo High School, a private co-ed school. He is living alone in a house owned by his uncle and his wife who moved abroad, so he asks a real estate agent to help him find a roommate. However, due to a mistake by the real estate agent, he ends up living under the same roof with a cute, innocent, but strong-willed girl named Kei Yamaba. Akimi Sugimura, a smart girl in his class, also takes an interest in Yusuke. While Yusuke deepens his friendship with Akimi, he is unable to give up his feelings for Kei, and is torn between the two. As the university entrance exam looms, Yusuke tries to find the answer about his relationship with Kei and Akimi, as well as his future career path.

(Source: Wikipedia, translated)