Isekai de Cheat Skill wo te ni Shita ore wa, Genjitsu Sekai wo mo Musou Suru ~Level Up wa Jinsei wo Kaeta

Tenjou Yuuya is a boy who has been bullied since he was a child.
He lives in the home of his beloved grandfather while he studies. As always, he is severely bullied and takes a long absence from school to have some time to heal his wounds.

During this long period of absence, he takes the opportunity to clean his grandfather's house and goes to a room that has never been before, where his grandfather keeps many different objects that he collected on his travels around the world. While he was arranging the objects, I found a door that was not on the wall between the objects.

Out of curiosity, he opens this door, what I found on the other side was …