Kono Kankei wa Gouhou desu!

A young man who is overly protective of his sister moves out to live alone in an effort to distance himself from her. He soon encounters a runaway girl named Ui, who behaves like a younger sibling and becomes attached to him. Despite her childlike appearance and mannerisms, she is actually a 19-year-old woman. As he tries to care for her, he faces internal conflict over how to properly interact with her.