Musou no Kaitaishi

Dungeons have suddenly appeared all over the world. People became "explorers" and dived into dungeons to obtain resources that could only be found there! Kurose Sakuto, too, was searching for the elixir that would heal everything in order to save his childhood friend who was suffering from an incurable disease. However, he receives a notice from his friends that he is no longer a member of the team. In the dungeon and in the real world, he faces off against demons and malicious humans.