Masato Wakamatsu lives in Tokyo with his step‑sister Miyuki, who is not a blood relative. Their father works overseas, leaving the two of them to manage on their own. Miyuki is cute, kind, and sensitive, and she is very popular among the boys who know Masato. At school, Masato has a girlfriend named Kajima Miyuki, a pretty and gentle girl who embodies the ideal dream of every high‑school boy.