Just bringing this up, because I haven't seen this blurb from 3.5 discussed in the context of Odin/Zantetsuken.
Spoilers: The Last Pillar to Fall
Unukalhai: "A magick was devised to contain a defeated primal's might within a stone known as 'auracite.' And the energies which bled from this imperfect vessel gradually corrupted the champions who wielded it. These heroes became slaves to an insatiable hunger for aether, eventually transforming into hideous fiends."
I believe this quote opens the possibility that Zantetsuken may be a primal trapped within auracite. The custodians of the stone may have wielded it as a weapon, and in doing so were corrupted by the energies it bled.
In the context of the FATE, it's probably assumed that there are a succession of victors who take Zantetsuken as their trophy after defeating its previous owner. They immediately become enthralled by Zantetsuken's power, and in the time it takes for the next FATE to pop, they are corrupted/transformed into a twisted likeness of Odin.