During my summer vacation, I was staying at my cousin's house in the countryside due to being a high school dropout. To refresh myself, I decided to spend some time alone there. It was during this trip that I met my older sister by marriage, Miho, who was ten years older than me. She jokingly asked if she could try inserting just the tip inside me, but before I knew it, we were having unprotected sex every day.

東京暮らしの僕（高●生）は不登校だった。リフレッシュの為に夏休み田舎の親戚の家で一人で過ごす。そこで出会った10歳年上の従姉・みほに「先っぽだけ入れてみる？」と冗談を言われ、本気にした僕はSEXを我慢できず暴走し毎日従姉に中出しをしてしまう。