The year is 200X. Jin (main character of Light Version), Akira (main character of Dark Version), and Lena are 6th grade friends who have grown up together. They are also members of the "Mystery Club" which searches for interesting and mysterious things. While snooping around the school's library, they happen upon a mysterious book containing various spells and incantations. Curiosity overwhelms the group as they decide to carry out a summoning ritual, unprepared for the consequences... To their surprise, an evil demon appears and their only hope comes from a peculiar new student, Amy, who gives Jin and Akira the power to capture and summon demons by way of the gun-like Demolyzer. They are also joined by Rand and Gale, guardian demons sent to protect them.