Fragile (ITOSUGI Masahiro)

From PROzess:

Sakurai Sakuya is a first-year student that hates summer. One day when he's verbalizing his hatred towards the sky, he is spotted by Kisaragi Haruka, a second or third year student. (It's only said that she's senior to Sakuya.) Haruka is the only member of the art club of the school and ask Sakuya to model for her. He agrees not knowing it would be a nude model. Sex ensues. Sakuya thinks that this is the end between them, but Haruka warmly sees him off with the words "See you tomorrow". Thus their fragile love begins.