The protagonist once had a girlfriend in high school. Unfortunately, the girlfriend later died under mysterious circumstances, and no one knew what exactly happened at the time. This incident became a thorn in the protagonist's side, making him unable to let go of it. One day, the protagonist suddenly discovered that he had the ability to travel through time and space. He then used this superpower to go back in time and conduct an investigation, only to find out that the murder was related to an evil serial killer...