Hyperspace

Hyperspace presents as a limitless, star-strewn void reaching past the everyday universe. Drifting through it are innumerable bubbles, and each single one holds its own reality, splitting off without end to cover every conceivable timeline, permutation, and variant of events.

The realm's defining trait is that it sits beyond the cause-and-effect order governing the ordinary cosmos. From within it, Void gains a sweeping overhead view that lets him scan and lock onto any point across the universe. A particular shinobi technique lets him reach out and make contact with the separate bubbles, and that contact is what powers his Dimension Slash, a strike he lands on targets in the physical world from wholly beyond it. He can likewise teleport to any spot he picks on Earth and could conceivably range across the whole universe from this vantage.

During the Ninjas arc, Empty Void slips into this dimension and hurls a Dimension Slash at the Hero Association Headquarters as a hostile greeting, only for Blast, present on the scene, to whisk the building clear of danger. He tries once more in the clash that draws in Flashy Flash and Speed-o'-Sound Sonic, aiming to kill Sonic and prey on Flash's grief, and again in his own duel with Blast, but each attempt is undone by Blast's well-timed teleports. Later in that battle Void slips back into hyperspace for another slash that would likely have killed all three, save for Saitama, who stepped in and dragged Void back down to the surface with his blade.