DEEP INSANITY THE LOST CHILD

A mysterious illness has put millions in comas. An underground realm has appeared at its origin: Antarctica. Strange creatures make up its population, and undiscovered natural resources make it a gold mine. Many humans enter in search of fortune, but Daniel Kai Shigure searches for something deeper—a cure. Gifted with immunity to the illness, he might be humanity’s last hope. (Source: Funimation) — Description from AniList community (anilist.co).