Tokyo en avril est...

Takizawa Kazuma, who returned from the United States, returned to Tokyo where he used to live, but unexpectedly ran into his classmate Ishihara Ren who hadn't seen him in ten years. Ren wasn't only Kazuma's classmate and first love, they were also each others' first sexual experience. It was supposed to be an exciting reunion after a long absence, but Ren showed an ordinary attitude and avoided talking about the separation... What happened ten years ago in the summer when these two separated?