Protagonists Ren and Rai fell prey to the Diabolo in an attempt to save the soul of Ren's cousin, 7-year-old Mio...although they failed in their attempt, they were 'rewarded' with powers they would each gladly trade for the life of the young girl.

Just who—or what—is the Diabolo? What enticements does he offer the kids at school? And, if they accept his 'bargains,' what foul fate awaits them on their 18th birthdays?