Deep Insanity: Nirvana

One day, a large hole named Asylum is discovered in Antarctica. At the same time, the mysterious coma-inducing illness Randolph Syndrome begins spreading around the world. Many countries sent an investigation squad to the asylum, believing it to be the cause of the disease, but not a single person safely returned. Sergiu Sol, a boy with a special resistance to the disease, and Antarctica's jack-of-all-trades Hildegard Olympiada Yamada, decide to take on the challenge of the large hole without a map, but...!? What is the cause of the coma-inducing disease? What in the world is the Asylum? Go down to the deep, jet-black bottom, one with insanity.

(Source: Square Enix, translated)