Based on the erotic game by Lune.

Shinji is a high school student. He loves Mayuri, his classmate. One day, a sick-room teacher, Ryoko, gives him a pendant. It seems people can have a good dream if they sleep with it. On that night, he goes to bed, holding the pendant.... A while later, when he wakes up, he finds himself being in Mayuri's room. Mayuri is asleep in the bed.... He gets sexually excited and has sex with her...! However, nothing is changed on the next day.... He is relieved and randomly has sex with other girls.... What's the secret of the pendant? What will happen to him in the end...?

(Source: ErogeShop)