Rui Tachibana

Rui is the younger sister of Hina Tachibana, but soon after Tsukiko Tachibana (Rui's divorced mother) marries a widower named Akihito Fujii, Rui becomes Natsuo Fujii's step-sister.

At first glance, Rui is an aloof and blunt girl who is hard to read emotionally. Her standoffish personality has made it difficult for her to socialize. As her first meeting at a mixer, she didn't do much to interact with the others. Once someone passes through her cold demeanor, Rui is actually a very kind and loving girl throughout the series. In spite of this, it can be hard for her to express her feelings towards someone she genuinely likes. She is very supportive of people she cares about, in spite of their flaws and even if their desires conflict with her own. Rui has a tendency to pout when things don't go her way, though Natsuo finds this feature of hers adorable. Rui is also surprisingly easy to embarrass in spite of her stoic personality. When Natsuo lists all of her behaviors he finds cute, especially to other people in front of her, she becomes overwhelmingly flustered.