S1·E40 No Shirt, No Shoes, No Assassins

It's revealed that Tojo and Suzuka know each other from the past, as they both underwent training from Saotome. Izumo and Tojo have a fight after school and Izumo reveals some of his demon powers. However Behemoth's 34 Pillar Divison has arrived and causes trouble. Aoi is captured by one of the pillars named Hecatos who wants to make her his contractor so that he can use all his powers in the human world. Oga and Hilda then fight together against him in order to rescue Aoi, however just before they believed they'd won Hilda is stabbed by Hecatos.