ダンジョンで成り上がれ！～幼馴染からも嫌われてゴブリンにさえ勝てなかった俺が、ダンジョンルーラーの指導を受けたら強くなれたので妹と無双します～

Synopsis

It has been 30 years since dungeons were established in Japan. Kyoichi has been accepted into the same extremely difficult high school as his childhood fiancée, Tsubaki, but... Rumor has it that he kneels before a goblin, and he becomes the target of class teasing. He tries to turn the situation around by exploring a dungeon, but is beaten up by a group of goblins. Thinking of his younger sister, Koyoi, he is ready to die, but... He is saved by a dungeon ruler named Kyoji. This encounter changes Kyoji's destiny.