The Grand Isekai War.

Isekai, the word that a character or characters are transported to another world via portal-quest, immersive, intrusion, liminal, or mainly get hit by truck-kun. It's where those of Isekai users who would change the balance of worlds. However, it appears that there's negative decision consequences in the Isekai worlds by both the protagonists and antagonists. As punishment, all of the Isekai users and those they've come across in every journey have been summoned to The Grand Isekai Arena for the survival of there worlds. However, upon being summoned to the next world, neither one of the different worlds of people would find themselves in more serious danger than they could possibly imagine.