Rui Tachibana

At the start of the story, Rui was invited by her classmates to attend a mixer. This was her first encounter with Natsuo Fujii, who was also forced to go. Likely due to the fact that they both were not used to that kind of situation, Rui and Natsuo left the mixer early with Rui wanting to ask him for a favor. The two end up at Rui's place, which is empty, and they head to her room.

Rui asks Natsuo to have sex with her - not because she likes him or wants a boyfriend, but because she wants to experience it for herself and is tired of people speaking to her condescendingly about it. After Natsuo gives an incredulous reaction, she explains she specifically chose Natsuo because he was obviously a virgin and didn't want someone experienced to take advantage of her or claim her virginity as a prize. Natsuo reluctantly accepted her reasoning, which led to their one-night stand.

After that night, both never met again until they found out that Rui's mother and Natsuo's father, both widows, would be marrying each other. Natsuo was especially struck dumb because his crush (Hina Tachibana) and his first in bed (Rui) would become his step-siblings. As their visit to the Fujii residence was almost over, Rui acknowledged her mother's remarriage and told Natsuo that, however awkward it may be for the two of them, she supports it because being with Natsuo's father has made her mother happy. Natsuo is then left to decide for himself whether he would support the marriage.

Rui, her sister and Ms. Tsukiko (Hina and Rui's mother) moved into the second-hand house Akihito Fujii (Natsuo's father) bought the next week. Natsuo and his father arrived later with the movers and all of the furniture and belongings. In the house, Rui eventually crossed paths with a nervous, agitated Natsuo. She asks him to forget that anything happened between the two of them and interact with her normally. A little later, after finishing house cleaning, the family gathered for dinner.