Quaetro Blitz (쿼에트로 블릿츠, Kwo-eteulo Beullischeu) is an D-rank Regular. Quaetro is assumed to be a male, however, SIU has stated that Quaetro's gender will be confirmed later on. Although he failed the test on the 28th Floor once, he appeared on the 30th Floor for the Workshop Battle. He is currently on board the Hell Express along with Team Tangsooyook en route to the 43rd Floor.