Continuing from Black Star Heart: Bloodlust. 

Gossip spread like wildfire the moment it had happened; Anri Eaton beat Marcus Swain into a bloody pulp on Leon Brackshaw's behalf one morning at school. So, the school dean enrolled them and their friends into the academy's Detention Unit Tournaments. Grueling real-life monster hunts to help level up their skills. However, the Swains are keen to satisfy their vendetta against Leon. A 10 million yen writ has been issued for his death.