The Necromancer Laughs (S01E04)

Ouka discovers documents detailing Mari’s offenses while in the chairman’s office. The following day, the Mock Battle Tournament continues into its second round, pitting Kyoya’s 15th Platoon against Takeru’s 35th. However, chaos ensues during the fight when strange black thorns erupt from Yoshimizu, Kyoya’s childhood friend and teammate! "I’ve come to save you, my dear Mari-san!" proclaims the necromancer, Haunted, as she emerges from the ominous thorns.