When Hina is caught, she doesn’t hesitate to be the adult and put herself at the mercy of her superiors. Sure, it probably wasn’t a good idea to sleep with a student in front of a window while on a school trip, but she doesn’t want that to affect her stepbrother’s future.
So she leaves the school, accepting a transfer far away, and then moves out of her apartment, all without telling Natsuo—who would have obviously tried to stop her and likely made things worse. That’s the second good move Hina made: not letting him have a say in the equation.
After reading a note in which Hina pours her heart out onto the page, Natsuo goes into a state of deep anguish, holing up in his room and not leaving. When Fumiya reads the note, he castigates Natsuo for basically wasting all of the pain and trouble Hina went through for his sake.
On a bathhouse trip with Kobayashi, the former yakuza and cafe owner tells him from experience that you can’t turn back time, and moving forward and continuing to live while shouldering his pain is the only way. But Natsuo manages to find an outlet for all that pain he’s shouldering: writing.
He stops his weekly short stories and instead starts pouring his heart onto the page, as Hina did with her farewell letter. At first it’s such a compulsive thing he doesn’t eat or sleep, but after his talk with Kobayashi he starts accepting Rui’s kindness in the form of cocoa, late night snacks, and other food to keep his health up.
On New Year’s Day, Natsuo finishes his novel, though he also lost track of the days. Rui takes him out where he meets with his friends from the lit club who were silently supporting him as he worked his shit out. Then they go to Kiriya-sensei’s house to deliver the first draft.
Some time later Natsuo is invited back to Kiriya’s on a Sunday, wondering what’s up. Kiriya has him meet Tsutaya, an editorial staff member with Shinkosha, and they go to a ceemony celebrating Natsuo’s first-place amateur award for his novel, which Kiriya secretly submitted.
Just as Hina had hoped, her quick action secured Natsuo’s future and ability to achieve his dream of becoming a novelist, even if it also broke both their hearts, those wounds heal, while a public school sex scandal…notsomuch!
When he gets home, Natsuo is shocked to find Hina waiting there for him…or at least he thinks it’s Hina. Turns out it’s Rui in a wig. She runs to her room to cry, because now she knows how Natsuo’s loving embrace felt to Hina. After congratulating him for his award, Rui has a proposition.
She’s done pretending to hate Natsuo, and she’s done “holding back” for Hina’s sake. When she and Natsuo made love for the first time, she didn’t think much of it, but she seems reasonably sure a second time will feel different to her, now that she has feelings for him and all.
Natsuo looks a bit overwhelmed, but if Hina truly is gone from his life forever, it’s a good idea to move on. Probably not with Rui…but I like Rui so, ah, well there it is. As Picasso said, “Art is born of your dad marrying the mother of the first girl you slept with and your longtime teacher crush.” Or something like that.