Space

Outer space, or simply space, is the vast and empty area outside Earth's atmosphere. It includes planets, stars, galaxies, and everything in existence of the One-Punch Man universe.

In order to find a worthy opponent that could give him a challenging fight, Lord Boros and the Dark Matter Thieves led by him travelled through space for many years via the giant spaceship. For that reason, Boros was known as the Dominator of the Universe. From an unknown place in the universe, it took Boros and his crew 20 years travelling through space to finally arrive on the planet Earth after speaking to an alien seer.

Normally, humans cannot survive in the vacuum of space due to the lack of air and the harsh environment. However, Saitama has been shown able to survive and adapt to the vacuum of space unaided.