Yuka Nakamura is the twin sister of Rika Nakamura and a childhood friend of Yuusuke Yamamoto. During their youth, Yuusuke saved both sisters from an attacking dog, causing each twin to develop strong feelings for him. Yuka specifically promised to marry Yuusuke when they grew up. However, in another childhood incident, she and Rika nearly castrated Yuusuke, contributing to his later fear of women.

As young adults, Yuka and Rika reappear at Yuusuke's home. Their arrival coincides with Yuusuke's father, a gynecologist, inviting them to live with the family in an attempt to cure his son's gynophobia. Yuka actively embraces this unconventional arrangement. Her personality contrasts with her twin sister's; Yuka is more outgoing, outspoken, and less reserved than Rika. She readily leverages her physical attributes to achieve goals, displaying confidence without embarrassment.

A significant development occurs when limited space forces Yuusuke to choose which twin can stay in the guest room. This triggers competition between Yuka and Rika. Both sisters employ various methods, including physical and personal advances, to win Yuusuke's favor. Yuka engages actively in this rivalry, demonstrating her determination and willingness to be forward in pursuing her romantic objective. Her actions throughout reflect her more assertive nature compared to Rika, who is depicted as comparatively modest and reserved.