Hero Association Defence Units

These robots exist as a tiered security system, with each machine slotted into a defence level that reflects how much force it can bring to bear. When sensors pick up a nearby Mysterious Being, the lower ranks launch first, and the network steps up to stronger models if the intruder proves too resilient. The system can leap past intermediate levels entirely once it registers an overwhelming opponent.

In the manga each robot carries a number matching its defence tier, while the webcomic leaves them unlabeled. Development cost was staggering, with a single unit reportedly running past nine billion yen. The higher-tier machines were believed powerful enough to have subdued demon-level monsters before Saitama ever crossed their path.

Designs shift dramatically from one tier to the next. A Level 1 unit is a bulky two-legged giant whose arms end in club-like Kanabo weapons, styled after an old Japanese bludgeon. Level 4 models switch to a four-legged frame that pins a target under a searchlight before opening up with head-mounted machine guns, a look drawn from the alien tripods of H. G. Wells' The War of the Worlds. The appearance of the second, third, and upper tiers stays a mystery, since those units were either never shown on the page or wrecked out of view.

The escalation logic is automatic. If the deployed rank cannot stop the target, the array immediately commits a heavier model, which is how it jumped straight to Level 4 after Saitama flattened the opening wave.

The units belong to their inventor, Bofoi, and to the Hero Association he built them for. Their most infamous encounter came as Saitama strolled back toward A-City alongside Black Sperm and Rover, two beings the robots correctly flagged as monsters. Saitama, assuming the machines were simply glitching and attacking him without cause, smashed the Level 1 units and then the Level 4 replacements with ease.

When association staff rushed out and complained about the ruined and pricey equipment, Saitama claimed the robots had spontaneously blown up, and King stepped in to keep him out of trouble. The incident dented the Association's faith in Bofoi. Reviewing the footage later, Bofoi was stunned to see every tier from one through ten destroyed, prompting him to quietly begin monitoring Saitama. The units resurfaced during the Robot Invasion, where they joined the heroes in fighting off the four million invading machines.