Tobi's first assignment as a Special Affairs agent lands him in Kaiei Academy's exclusive Invitational Class, a gathering of zingai-aware students kept separate from the rest of the school and showered with special privileges. But as it turns out, the price for this treatment is steep: They must risk their zingai in Invitational Battles, where the rule is eat or be eaten! Even stranger, the defeated students quickly return to class, and while they are changed, they don't appear to be spirit-hollowed. Could their secret be the key to finding a cure? Something weird is going on at Kaiei, and here, too, Tobi feels the shadow of his brother, the mysterious man known as "S"...