Nankatsu Industries is a very advanced technology corporation in Japan. It collaborated with the Blackdoor Group to help destroy the Immortal civilization by supplying test subjects and weapons. The Immortals' rebellion forces broke into the Nankatsu Advanced Materials Laboratory to steal a data file to discover where two superbeings encountered in India came from. Also, they found a sarcophagus-shaped keyhole within the laboratory, where they escaped to the Nankatsu Submersible Proving Grounds. Nankatsu built the Hei Ten Shi and the Idrasil.
There is evidence of close collaboration between the Edeners and Nankatsu; the Advanced Materials Lab had a functioning keyhole linking it to the Submersible Proving Grounds. They also evidently know about Leviathan, having sent and developed the Hei Ten Shi to reach it.