Tensei Shitara Ken Deshita: Another Wish

In the manga's story, the cat-eared girl Fran and the man reincarnated as a sword she calls "Teacher" take on the Phantom Dungeon, which appears only once every three years. In the innermost area of the dungeon, the pair discover a mysterious bell suspended in the air. When they smash the bell, a mysterious light envelops them. After coming to, they realize they've been transported to an unfamiliar place. Something seems off with that world compared to the world they were just in.