The story takes place in the Tenshō Era of Japan. Usagi is a bumbling ninja-in-training in her village in southern Iga. Though she is already fifteen, she is a terrible ninja and has made no progress whatsoever. As a result, her grandfather gives her a special mission: to go to Segachi, marry Hanzō Hattori, the leader of the main branch ninja family, and bear his child. She is accompanied by Mamezo, her longtime friend, companion, and foster child. Once they arrive it becomes apparent that Hanzō has no intention of marrying anyone, and worse yet, it seems Usagi has a much more refined rival. It is clear that as Usagi spends more time with Hanzō, she is growing on him, though the fact that he is constantly bombarded with new potential brides makes Usagi self-conscious.
