Natsuo is bowled over by the Japanese American transfer student Alex, who is biking indoors, and the two end up apprehending an underwear thief who stole from Rui, among others. At the police station, Al sees Rui and immediately asks Natsuo (who calls her “a friend”) if he’ll set him up with her.
This, when Natsuo is still trying to figure out how he feels about Rui, who is affectionate when they make out but otherwise her usual stoic, hard-to-read self. While making dinner, Natsuo comes right out and asks Rui if she’d want to hang out with him and Alex. she sees right through his feeble ploy, and storms off, positively furious.
He visits her room later with a peace offering of yaki-udon and an apology, but Rui wants him to apologize by kissing her. The two are closing in on second base when Hina enters the unlocked, slightly open door and sees the two embracing.
After a long, agonizing pause, Hina flees to her room, and when Natsuo tries to explain, she tells him she’s not in the state of mind in that moment to believe anything he says. Instead, she declares that she needs to stop living there.
Rui visits Hina and explains that she initiated things, because she’s pretty sure she likes Natsuo. When Hina brings up the fact they’re family, Rui doesn’t see a huge issue, since there’s no blood relation. Nevertheless, Hina thinks their mother would be sad.
Al gives Natsuo the advice that nothing will ever be solved if nobody talks to each other plainly and honestly about how they feel, but the next day Hina announces she’s going to move out and live on her own. Her mom and stepdad buy her explanation, but Rui and Natsuo suspect they’re to blame (obviously).
The entire family goes to a night festival while Hina is still around, and Rui wonders if she and Natsuo should cool it with the kissing for the time being. Meanwhile, Natsuo can’t stop looking at Hina’s nape. When Hina loses her cell phone, Natsuo takes her by the hand and leads her to a private place where they can talk.
But Hina remains evasive, other than to say it’s necessary for her to move out for both their sakes. Natsuo’s attempts to force an honest conversation backfire badly, when he refuses to let go of a Hina who’s clearly had enough, and she bites his hand. The manager listens to Natsuo and holds Hina in place, noting how ugly she looks when she’s angry (his response when she says she’s always ugly is both brutal and hilarious).
The manager, one of the waiters, and her young son all join Natsuo and Hina in another secluded spot so the latter can cool down, but she’s tired of being the adult, and starts acting like a child. The son offers her a lollipop to cheer her up, and it largely works.
The manager, waitress and son depart, and Natsuo listens as Hina explains how it was just as much jealousy as shock when she say him with Rui. Rui has always been a free spirit, so Hina always felt she had to be the “normal” one who “kept it together”, not simply shooting from the hip like her little sister. She sacrificed her grasp on her identity, in part, to protect Rui’s.
Even though Hina rejected him, she did so because she felt she had no choice; as the adult in the room, she couldn’t give in to her feelings, no matter how real or strong they were. Hearing that his love isn’t unrequited after all is a revelation to Natsuo, who embraces her and asks nothing more than to be able to hold her like that and say that they love each other for that brief period of time.
As the family heads home together, while Rui isn’t turned around and looking, Natsuo and Hina hold hands. So it would seem that Natsuo is choosing a sister, based on his longstanding feelings for Hina. But just because he now knows those feelings aren’t one-sided doesn’t change the fact that Rui has fallen for him, and he’s going to have to address that every bit as earnestly as he and Hina addressed where they’re at. Because one thing is certain: Rui ain’t dating Alex!