Overgrown Rover

Rover is an enormous black hound with six glowing, ruby-red eyes, oversized fangs, and four-toed paws. Shaggy, unkempt fur mats its outer body, while the inner parts show bare muscle, and it has neither visible ears nor a nose. Once the Monster Association falls, the beast dwindles to the size of an everyday dog.

At heart Rover behaves like a guard dog, dogged and loyal, hunting Garou down without pause once the Hero Hunter crossed it. Harsh conditioning taught it to obey a "sit" command even from an enemy, which both Saitama and, later, Bang exploited to make the Dragon-level beast drop and stay. It does not attack every intruder on sight, leaving Garou and Tareo be when they backed away quietly, yet in a rage it lashes out at anything, even killing its ally Unihorn over a stray blow.

After Saitama beat and cowed it, Rover feared him enough to flee rather than follow Orochi's order to attack. Shrunk down, it turns thoroughly gentle, sniffing and licking Saitama much like an ordinary pup and showing no hostility even when the heroes pick it up.

Posted to guard the Monster Association headquarters, Rover first crosses paths with Garou and Tareo, then joins the fray to blast apart several Demon-level monsters and pound Garou with point-blank energy cores. Saitama later stumbles onto it, dodges its blasts, and punches it into submission with a single "sit," a blow that rocks the whole base yet leaves it alive. Recognizing the bald hero afterward, it flees him mid-battle, baffling Orochi. When Do-S sounds a dog whistle, Rover is drawn against Bang, Bomb, and Fubuki, and only Bang's offhand demand that it sit finally halts its rampage.

Once the association collapses, Rover mysteriously shrinks and becomes Saitama's pet, entrusted to Forte, Chain'n'toad, and Butterfly DX, briefly adopted by the Blizzard Group and later helping fend off the Dragon-level Mirror. Its power centers on rapid energy bursts fired from its mouth that can level city blocks, backed by immense strength, durability that weathered Saitama's punch, speed enough to match half-monster Garou, and keen canine senses of smell and hearing.