While the class begins to make steady progress on clearing the Underworld—the great feat they have chosen for their attempt to become Sages—not everything is going smoothly. Ayaka Shinozaki, a classmate long thought dead, has reappeared in the city and is hunting down members of the class one by one as revenge for abandoning her back on the bus. At the same time, a mysterious organization has once again begun targeting Yogiri, making attempts on his life every time he leaves the castle. And just when the class thinks they've tracked down the culprit, a ghost from Yogiri's own past enters the stage, throwing even our calm and collected protagonist into a state of shock.