Yuuki Fukuzawa is the younger brother of protagonist Yumi Fukuzawa, attending a different school while maintaining a close sibling bond with her. In the second OVA, Yuuki engages Yumi in a conversation about her preferences, specifically asking about her "type." When Yumi describes someone who is pretty, smart, and outwardly seems to have a warped personality but is warm-hearted inside, Yuuki immediately recognizes this description matches Sachiko Ogasawara, Yumi's grande sœur, pointing out the similarity to Yumi's surprise. This interaction highlights Yuuki's perceptiveness regarding his sister's feelings and relationships. Primarily, Yuuki serves as a supportive presence in Yumi's life, offering incidental yet insightful commentary on her personal growth and her connections within the Yamayurikai. His limited appearances provide contextual understanding of Yumi's character development through these familial interactions.