After the sudden death of their parents, Haruka and his twin sister Sora move to the house formerly inhabited by their late grandfather, in a small village they often visited as children. There, Haruka encounters several of the residents, some of whom are old friends, but Sora stays at home, refusing to go to school even as Haruka starts attending. Realizing that Haruka is growing more and more distant and slipping from her grasp, Sora goes to Haruka's room at night and appeals to Haruka as she removes her clothes...

Sora asks Haru to take her measurements so she can have a uniform made, and finally starts attending school with Haruka, though she is disappointed to find that she and Haruka are in different classes. While cleaning the swimming pool as part of a mixed gym, Akira accidentally soaks Kazuha who forgot her swimsuit, and so Akira takes her to dry off. Haruka finds Kazuha's phone and goes to return it, only to overhear a sensual-sounding conversation in which Kazuha addresses Akira as "Onee-chan" (big sister).

Haruka is standing near the girls locker room, overhearing Akira's and Kazuha's conversation. Haruka notices that Akira has been acting strange lately, and decides to talk to her alone at school the next morning. He sees the sad look on Akira's face and becomes worried, and wants to help Akira find her mother's pendant (after remembering her losing it as a child). They go in search for the pendant by a tree they would play by as kids, only to Haruka's horror that the tree had been removed by a landslide. He attempts at digging around for it, but without any luck. The two go to Akira's to take a bath, and have a romantic moment together. From there, Haruka goes to the festival, and, after seeing Akira cry while dancing the sacred dance, rushes off to see what had happened.

Haruka enters Akira's room and stops her from burning something, which is her mother's missing journal, where it is written that Kazuha and Akira has a chance of mistaken identity. With the journal, he suggests to Yahiro and Kazuha a DNA test to prove things once and for all.