Yaji to Boku

Taro is a researcher working to enhance animal intelligence. His experimental rat, Yajiro, is accidentally released by Taro's mentally handicapped brother, also named Yajiro. The rat is then adopted and named Yaji by the boy.

Yaji begins to display remarkable intelligence due to Taro's experiments, leading to unexpected situations. As the bond between the boy and the rat deepens, Taro must confront the consequences of his research and the ethical dilemmas it raises.