ダンジョンの測量士～地図で無双するダンジョン攻略～, Surveyor inside the dungeon, Danjon No Sokuryoushi ~Chizu De Musou Suru Danjon Kouryaku~

The "Dungeon Map" is indispensable for dungeon conquering. Who on earth drew this map? Daria, a failing E-rank hero, aims to conquer a high-difficulty dungeon that still lacks a map, but she ends up wandering alone. In that dangerous dungeon where monsters nest, a man collapses. The identity of this middle-aged man, who says he was just suffering from a hangover, is Graham, the legendary hero who was the only human to ever come close to the Demon King. And in his hands, he has a piece of paper and a pen……?