Before joining the SSS, Shiina lived in the deepest underground level, a place not yet controlled by the guild. Yuri and Noda refer to Shiina as the “underground” or the “final” boss, because their first meeting resulted in bloodshed. Shiina also attacked Oyama, Cha, and Hinata relentlessly and the group was only able to escape her wrath by returning to the Afterlife School where they regrouped and planned a counter-attack.
Cute cosplay! But with that look in her eyes, I don’t think I’d want to mess with her either. Thanks to anon for sending this in!