Squad Zero is a branch of Troop Mizoras Enforcement Corps for VIUS and is commonly known for taking on dangerous missions, with its Squad Captain, Kazuma Issa, being detested. Squad Zero was mysteriously disbanded and later re-established after an initiation test.
Old Squad Zero
Old Squad Zero consisted most notably of Sakuraba Shun'ichi, Ran-Ran Yume, Rokurō Hyuga, Rin Kyōko, Hibiki Masamune, Shinobu, and Kiura. The Squad was however disbanded after an incident involving Kazuma going berserk and attacking one of his own Squad mates because of his Dragon Eye, killing Kiura in the process.
New Squad Zero
For the next seven years, Squad Zero would be disbanded until Kazuma would take on the role of an enlistment instructor for an examination regarding several new VIUS cadets, activating his Dragon Eye and saving the life of Leila Mikami in the process. Though being lectured for his use of the Dragon Eye, the squad would be reinstated. Their first mission would be to wipe out a horde of Dracules that have begun lairing in the underground area of District 4 of the Old City, joined by volunteers Hyuga from the Intelligence Corps, Hibiki Masamune from Squad One, and Yukimura Sōsei from Squad Five. During the extermination, it is revealed that Yukimura is the brother of Futaba, a victim of the D-Virus that was killed by Kazuma during his earlier missions six years ago. Taking the chance, Yukimura attacked Kazuma and proclaimed that he will subject Kazuma to a fate worse than what he made Futaba suffer, however, the fight is defused after asking Yukimura if he wanted to join Squad Zero.
After the extermination and the consideration, Yukimura takes Kazuma up on the offer, joining Squad Zero after consulting Sakuraba. Their next mission would be within Mikunis District Three First Avenue, investigating the illegal transportation of the D-Virus for black market purposes. After chasing down the perpetrator, a spherical confinement note spell unravels itself, revealing itself to be a Bird Monster-Form level 2 Darkness-hued Bird referred to as Kaligera. Having his other teammates retreat, Kazuma battles the Kaligera alone with Squad Five concealing the truth, evacuating and protecting the area with spell notes and spell castors in a hexagonal cage, Kazuma defeats the Dracule after leaving the leaving the city limits with the Dracule and using his Dragon Eye after learning of the existence of the Daraku, a mysterious third party attempting to breach Mikuni. The mission would later be confirmed and backed by Captain Kiura of Squad Five, despite the judgement of leader of VIUS government.
Punishment for his reckless actions, Kazuma is strapped to a crane atop a building by Sakuraba before being released in a sickened state from the height. In a hasty emergency deployment in Center Hall B5, Squad Zero would join volunteers Kajiyama of Squad Two, Sazanami of Squad Three, Nanbu of Squad Seven and sub-commander Hibiki Masamune in a mission to investigate several large Dracules in the outskirts of Mikuni, leading them to their undertube vehicle being derailed during an earthquake and the investigation taking a turn for the worst when their search would take them deep within the caves nearby. Kazuma and Yukimura would later be separated from the rest of the team after a cave in, leading them to discover a meeting between the massive hordes of nearby Dracules and the mysterious Daraku. While Yukimura, Leila, Sazanami, Nanbu, Kajiyama and Hibiki are forced to battle against Level 3 Shrew-Like Dracules, Kazuma and Yukimura fend off a never ending force of Dracules, forcing Kazuma to don a mask, referring to himself as Leda, a powerful rank of warrior in the Dracule army, intimidating the horde while the other group successfully escape the caves. Finally making their own way out of the caves, Yukimura and Kazuma swear that what they witnessed will never be put in the reports, despite Hibikis suspicions.
Kazuma Issa - Squad Zero Captain