Shin'ai naru Boku e Satsui wo komete

Urashima Eiji, a college student, goes to sleep after a fun drinking night with his friends. When he wakes up he discovers a beautiful girl next to him who treats him as if they are in a loving relationship. Later, Eiji finds out that 4 days have passed since he went out with his crew. What did he do during all that time and why does he have no memory of it? By confronting that reality, he will be caught in tragedy...