The Ariake Seal (in Japanese: 有明・結界； Ariake kekkai; Ariake barrier formation) was a barrier that was created by Kagari Ubusuna, who acted under direct orders from the Japanese government to seal Akujiki and prevent the Hellspawn from returning.
Formation of a Seal
After his final confrontation with Hiruko, Hotsuma willingly ended his life by allowing the crumbling Golden Palace to swallow him. Not only was he disgusted with the thought of living for nothing more than to feed Akujiki, he also hoped that the crumbling tower would destroy the sword along with him. Therefore, Hotsuma remained inside the palace as it collapsed around him in order to both free himself from the blade's curse and destroy the blade. When government agents arrived on the scene, they conducted a thorough investigation of the ruined site. The agents found nothing but the demon sword Akujiki among the debris.
Since ancient times, the sword has brought great calamity. Said to grant it's wielder immense power, Akujiki's curse has claimed the lives and souls of countless men. For decades, the Oboro clan valiantly fought to end its bloodstained legacy. To ensure that Akujiki may never again bring forth chaos, and to prevent the return of the Hellspawn that were attracted to Hiruko's lingering dark energies, the Japanese government ordered Kagari Ubusuna of the Ubusuna clan to seal the demon sword away.
The young priestess used the teachings of the Ubusuna's onmyoji and performed a ritual that would seal the blade. She broke Akujiki into nine shards and scattered them throughout Tokyo. She placed sacred jade mirrors that were powered by Yang energy in various places around the barrier, and the Ariake Seal suppressed the Yin energy that powered the portal between the Earth and the evil Hellspawn realm and kept their gates sealed.
However, the Nakatomi Conglomerate desired Akujiki. In their greed, they sent their forces to break the seal and steal the shards from the fortification, which resulted in an outbreak of even more powerful Hellspawn that were imbued by the blade's dark energy.