Basement Dungeon ~ Poor Siblings Seek Entertainment and Become the Strongest ~

One day, dungeons appeared all over the world. Creatures gushing out from the dungeons trampled nearby humans and animals. However, the UMAs, or monsters, that emerged from the dungeons seemed to lose their power as soon as they left, and were quickly annihilated by the country's modern technology. Even in countries with insufficient weapons, there was chaos, but the monsters that appeared on the ground were weak and were exterminated by people who had been trained in their daily lives. Swift measures were taken, and the world regained its safety. Afterwards, a certain country discovered resources within a dungeon, changing the world. This is Japan. The opening of the dungeon brings about episodes of laughter and emotion. Meanwhile, in the countryside, a poor brother and sister, whose parents have disappeared, live in a dilapidated house. They discover a dungeon that suddenly appeared in their basement and explore it for entertainment. This is their story.