Sekai de Yuiitsu Dungeon Saikasou ni Toutatsu Shita Otoko, Bishoujo Haishinsha ni Sarasareru

The lowest level of the dungeon beneath Shibuya...a realm never before reached by humankind. Despite being a dungeon, it has forests and lakes, and day and night. There, a college student adventurer named Shiraki Minato, who was enjoying a slow life in a log cabin, rescues Minami Rei, a beautiful girl dungeon streamer who has wandered into the underworld level. Minato becomes an overnight sensation as the man who conquered the underworld level, and together with Rei, he begins to compete against adventurers from Japan and overseas.