Meikyuugurashi no Boukensha wa Dungeon Master wo Yametai

Wade, an adventurer specializing in labyrinths, has come to a dungeon to obtain a detection artifact in order to seek revenge for his friends. He enters the dungeon with an exploration party commanded by a nobleman, but a huge dragon blocks their way, and they are wiped out... Wade fights the dragon with determination, but he is defeated and fatally wounded. However, when he wakes up, his wounds are completely healed, and he has become a dungeon master...?! The labyrinth defense tale of the adventurer trapped in a dungeon begins!

(Source: Takeshobo, translated)