Who Designed This Underworld Dungeon? - Chapter 33 - Rebirth by Borrowing a Body Technique

The World of Immortals, it is the world every mortal long for. For many, it is an eternal glory to cause a spatial distortion and enter the World of Immortals. But the vicissitude of time is simply merciless, the legends regarding immortality had long been forgotten.

After coming out of a tunnel… it was pitch dark.

Protagonist travels between different anime worlds to right wrongs and uncover his reason for being along the way.

The world was once at war with 10 alternate worlds. This was known as the Concept War and our world won 60 years ago. All of this was concealed so no normal people are aware of this fact in the current time.

After the death of his grandfather, the high-school student Sayama Mikoto is suddenly summoned by the giant corporation IAI. He learns this world is headed for destruction due to the acceleration of the Minus Concepts. To prevent this, negotiations must be undertaken with the survivors of the other parallel worlds so their 10 concepts can be released.

And so Sayama is caught up in the final battle to clean up after the Concept War which left behind so much enmity.