Kippei Katakura is a seventeen-year-old flirt with more interest in chasing girls than in anything else, until his aunt disappears and leaves her five-year-old daughter Yuzuyu with the Katakura family. Kippei is handed the job of looking after her, and the round-the-clock work of feeding her, walking her to nursery and calming her crying forces him to grow up fast. Helping him through it is Kokoro Tokunaga, a reserved classmate who steadily gets closer to him.