Ash

What Fire leaves once the living force is drawn out of it. Ash is the plane of the ended cycle and, by the reckoning of its own god, of what comes back through the ending.

Hikāru holds it: the Ashen One, the Phoenix of Rebirth, the Undying, who ascended when only Jerta remained of the elder inner-planar gods. Their worshipers divide sharply: some are drawn to the destruction and some to the regrowth, and the faiths have never reconciled the two readings.

The Elder named the plane at the Twisted Grove (S3E38), beside Radiance, its opposite, and empty.