Separation picks up where episode 2 left, with Kaoru hearing Aoi outside his bathroom, offering to wash his back.
Kaoru, thinking that Aoi has undressed, tries to keep her from coming in, but she comes in, anyway, surprising him by still being dressed, and then embarrassed.
Suddenly, the door opens and another, older woman comes into Kaoru’s apartment, throwing him away from Aoi.
Aoi introduces her to Kaoru as Miyabi Kagurazaki and it’s revealed by her that Aoi had left home without telling her parents where she was going.
Aoi wants to be married to Kaoru, but her family forbids it due to him leaving the Hanabishi clan and having no means to provide for them. Aoi tries to convince Kaoru to return to the Hanabishi, but Kaoru stands firm in his decision not to return. He later explains to Aoi why he can’t go back to the Hanabishi: It turns out that his parents were never married and when his father died in an accident, his grandfather, the current leader of the Hanabishi, wanted to take custody of Kaoru to teach him to be the next leader of the Hanabishi. His mother, wanting only for Kaoru to have a good life, gave him up to his grandfather.
However, Kaoru couldn’t deal with the harshness that his grandfather dealt him while living with the Hanabishi, and left after an altercation that resulted in his grandfather scarring his back with his bamboo cane after his mother died. Because of his harsh upbringing by the Hanabishi, Kaoru refuses to go back to them, no matter what anyone says.
Aoi now understands his reasons and accepts his decision.
The next day, Aoi and Miyabi leave to return to the Sakuraba family, but later that day, Aoi calls Kaoru after running off from Miyabi and getting lost again. Kaoru comes to get her and it starts to rain. They go back to Kaoru’s apartment and Aoi tells Kaoru that she has decided to part ways with her family just like he did with the Hanabishi, even if it means giving up everything as long as she can be with him, and then asks him to exchange vows with her.