Onk'ar Decath

Onk'ar Decath opening on Phlegethos

The Onk'ar Decath rift was created in secret by Asmodeus's most loyal confidants. It was built as a line of retreat if he had a falling out with the angels. He had reason to suspect he would because of his methods in dealing with the demons. In the Demon Spawn War, Asmodeus was for a time the supreme leader of all forces of the Quara'tun Covenant. Even though he was their supreme leader, his war practices on planes like Avernus and those of the Abyss were coming to attention of the more goodly angels and gods. These practices included torture, utter soul destruction, genocide against the demons, and putting non-demon allies in labor camps with often inhumane conditions. Spies had also learned that he was diverting souls destined to the Abyss and redirecting them to Baator where they were drawn into an illegally modified Well of Afterlife. The demon souls that were drawn here were changed in alignment to lawful neutral or driven insane in the process. The insane ones were still chaotic evil, and now in their maddened state too dangerous to keep around, so they were terminated. The sane lawful neutral ones were pressed into service and sent back to the battlefields of Avernus and other battle areas outside of the Prime.

At the time, the plane Baator was lawful aligned and not a Soul Gathering Plane. When Asmodeus became a Fallen Angel, Baator became better known as the Nine Hells, and became the soul gathering plane for lawful evil souls. It replaced Gehenna which had originally been set by Io as the plane for such souls. Io helped Asmodeus in this undertaking since not even Asmodeus and all the magical might of his followers could move the Well of Afterlife to Baator. Io's helping Asmodeus was done out of practicality since the angels and gods alone were not enough to counter the vast demon population of the 666 planes that made up the Abyss. When the work was done of making the Nine Hells the destination for the lawful evil souls, Asmodeus completed the deal by handing over the modified Well of Afterlife that he used in the Demon Spawn War.

 - Melek Taus, contract historian for Asmodeus - "Baator Deal"

When Asmodeus was cast out, the rift Onk'ar Decath was hidden with powerful magic. It was kept a secret by Asmodeus with him eliminating all those that had a hand in building it. Asmodeus used this rift to send agents to Bal-Kriav where they spread his influence surreptitiously. In the Horgon Era, he sent the tieflings through the rift where they built the settlement Kathodrarg. They built a temple to Asmodeus with the mouth of the rift as the altar. This transplanting of outsiders did not go unnoticed by the gods. Athena worked out a deal with Loki whereupon they sent agents into the temple who then planted a Null Mine inside the rift. When the mine detonated it permanently closed the rift.

In the Nine Hells, the rift is on Phlegethos. This side of the rift is still open, but goes nowhere. The rift's opposite end is on Bal-Kriav, in the labyrinths under Kathodrarg. Where the gate opening once was is now a Sphere of Annihilation locked in place by divine magic.