Cousin Wataru who casually encounters drunk sister after drinking party. Two people who resumed their first appearance in about ten years have decided to spirit and exchange sake. Watar surprised by the appearance of her sister who was totally grown up while not watching will miss the last train with a memorable story. Wataru who was supposed to be stayed in the room where the sister lives also because there is a thing close to the station Three people are sleeping in the same room ... Moreover, in the character of the river. Wataru who saw her older sister sleeping in an unprotected appearance hugs her sister without getting excited. My older sister who desperately suppresses her voice so that she can not get her sister. However, my sister estrus when hearing her squirming voice. Wataru who ended the sister with her sister realized that her sister was up and was excited and this time she tries to hand out her sister! The urge of sister rice bowl that does not go beyond ... Still this situation can not be closed afterwards! I can never taste it again! What action Wataru has taken on the perfect opportunity brought by chance 飲み会帰りに酔いつぶれた妹と偶然にも出会う従兄のワタル。約10年ぶりの再開を果たした二人は意気投合し酒を交わすことに。見ない間にすっかり大人びた妹の姿に驚くワタルは思い出話で盛り上がり終電を逃してしまう。駅から近い事もあって姉妹の住む部屋に泊めてもらう事になったワタルは、信用されているのか3人同じ部屋で寝ることに・・しかも川の字で。あまりに無防備な姿で眠る姉を見たワタルは、興奮を抑えきれずに姉を抱いてしまう。妹にバレないように必死に声を抑える姉。しかし妹は姉の喘ぎ声を聞いて発情してしまう。姉とヤリ終えたワタルは、妹が起きていた事に気づき興奮して今度は妹にまで手を出そうとする!超えてはイケない姉妹丼の衝動・・それでも後には引けないこの状況!二度と味わえない!偶然がもたらした絶好のチャンスにワタルがとった行動は!?