Xenoverse

The Xenoverse, or X-Verse, is a set of realities where 12 universes reside. However, the creation of time travel expanded to hundreds of thousands of universes.

The Tournament
Before the effects of time travel were found out, a tournament between the Sixth Universe and the Seventh Universe was held. The tournament ended with the Seventh Universe's victory, but it resulted in a wave of multiversal tournaments that eventually became one enormous tournament.