Universe 5 is one of five universes in the Epic Multiverse. It is the least populated universe, containing only Universia, though it did once house inhabitants.
When the universe crossers went into Universe 5, there were only two beings left, Star-K and Naught. Naught is said to be the most powerful of all the Seventy-Fives, with Star-K being about equal to him, it seems. Naught scolded Star-K for bringing friends (even though they weren't), but fought them all anyway. He killed Malleo, which caused Deegee to get enraged enough to reach his god form. The heroes easily defeated Naught afterwards.
Since Star-K went to Universe 1, Universe 5 is completely empty. Zeno used it to trap Universia, although he already figured a way out.