Isekai De Cheat Skill Wo Te Ni Shita Ore Wa Genjitsu Sekai Wo Mo Musou Suru Level Up Wa Jinsei Wo Kaeta

Tenjou Yuuya has been a bullied boy since the past
He lives in the home of his beloved grandfather while he goes to school As usual he receives a harsh bullying and he takes an extended absence from school to have some time to heal his wounds
While on this long time of absence he takes the opportunity to clean his grandfathers house and goes to a room he never went before where his grandfather keep many different objects that he gathered from his travels around the world While he was arranging the objects he found a door not on a wall among the objects
Out of curiosity he opens this door what he found on the other side was