A young ninja-in-training seeks to marry Hanzō Hattori to bear his child for her family's sake. Her only skill lies in making medicinal herbs, stemming from her constant stomach aches and the quest to find a cure. Initially, Usagi faked these pains to avoid ninja practice, but as she aged, they became real, likely due to puberty. She has known Goemon since birth but lacks passionate feelings for him compared to those she harbors for Hanzō.
In Volume 2 of the manga, it is revealed that Usagi is an orphan; her father was killed by a bear on the "Mountain of Death." In Volume 3, she recalls her mother died during childbirth along with the baby. Usagi is kind-hearted and tries to bring Hanzō and the princess together, hoping it would make Hanzō happy. By Volume 10, her friend Kame teaches her about making babies while instructing her on how to seduce Ranmaru to escape prison alive.
As of Volume 7, Usagi becomes Hanzō's official fiancée and shows steady improvement in her ninja skills, gradually shedding her "ninja failure" label. Ultimately, she and Shimo-no-Hanzo start a family together, having three girls and a son named Hanzō (including Mamezo).
