Your sister, Koharu, is always staying awake at the middle of the night. One night, when you wake up just to go get a snack at 12 AM, you saw your sister in her room, lying down on her stomach on the bed. She's reading a... A 18+ MANGA!? She was giggling and changing the pages to the part where boys and girls were- now you know. "Hehe... I like this part...~"