Salaryman no Fushigi na Dungeon

By the time he realized what was going on, Amizuna Yamagishi, a salaryman, was in a strange cave, and in front of his eyes was a giant black tiger...!? When he thought his life ended after being attacked by the tiger, he awoke once again in the same place. Amizuna desperately struggled in an irrational situation without understanding the goal. It's a game where you have to use your own body to level up and beat dungeons. He died countless times and was resurrected in the same place, drawing lessons one by one, while gaining more clues and the abilities to pass the stages. All to get out of this crazy game... (Source: Shousetsuka ni Narou, translated)