Overgeared - Chapter 15

A world filled with heroes with superpowers. A world attacked by calamity fiends. A modern world filled with wonders and dangers.

Zhou Yu, a reclusive otaku, who did not like to go out of his house, was one day forced out of his house by a series of unexpected events.

- Description from Novelupdates

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.