A high-school student and skillful computer programmer named Akemi Nakajima created a software called "Devil Summoning Program". At first Nakajima intended to use the software to gain revenge on a classmate who bullied him. However, things went out of control, and the malicious demon Loki was unleashed into the world. Soon, a demonic invasion of the Earth began. Aided by the lovely Yumiko Shirasagi, a transfer student who seems to be interested in him, Nakajima decides to undo his wrongs and defeat the demons. In order to do that, the young couple will need to learn how to use the program for good purposes, and uncover the truth about their own previous incarnations.