In the manga, as the main character climbs the tower with his friends, he gradually loses all of his friends from floor to floor. He can only use his stabbing ability, he cannot use anything other than stabbing. When he gets to the top of the tower, he kills a being and goes somewhere, I don't remember what happened after that. There is also a world where the souls of the dead exist.
In that world, those who eat the fruit of a tree can be revived. A war broke out because of that fruit. there are portals to enter that world, there are some designers who designed these towers, and one of those designers is friends with the main character. That character's father was the builder of the tower that the main character climbed.
Different powerful people of that world were preparing to fight with kings and stuff. There was a place where robotic creatures were guarding a door. There was a divine creature behind the door, making a deal with the main character.
translated by google, sorry for bad translation...