Sonic's Hideout

The site is a run-down building at an undisclosed location that the story never pins down. A stretch of woodland grows close at hand, and Sonic frequently retreats there to sharpen his skills.

Sonic leaves this refuge to drill in the forest, where two elder graduates of the Ninja Village, Gale Wind and Hellfire Flame, hunt him down and pitch membership in the Monster Association, pressing a monster cell into his hands. Back home he broods over his inability to eclipse Saitama despite relentless practice, then resolves to consume the cell.

Later, during the Ninjas Arc, the Heavenly Ninja Party corners him at the hideout and orders him to bait Flashy Flash to the spot. Empty Void afterward perches atop the roof only to be crushed the instant he swings at the arriving Saitama. Blast's portal soon gathers Saitama, Overgrown Rover, Flash, Sonic, and the ninja party together here, and when Byakko and Genbu erupt from the Rift in Spacetime, the pair wreck the building and surrounding city blocks before Blast and Void banish them.

In the webcomic's telling, A and twenty-nine subordinates later ambush Sonic on the premises hoping to seize his body for the Neo Heroes, but he wipes out every attacker and forces A to retreat.

The hideout's emptiness echoes the state of the Z-City Ghost Town. Volume 15 appears to show a toilet that Sonic makes use of somewhere inside the building.