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Originally in CT, the Susanoo Unit was merely a suit, but a few things concerning Hakumen was retconned after that. In CT, Hakumen was the result of the Alt End which Jin falls into the Cauldron, but that was retconned as well. Hakumen came as a result of a completely different Jin in a different timeline where Noel didn't exist, falling into the Cauldron.

The importance of this is that the Jin from that timeline got his body ravaged extremely because of travelling through the Boundary, and ended up wheelchair-bound as a result. Clavis, Rachel's father, offered the Susanoo Unit to him as a new body to use because of it, as he had it locked away.

The Susanoo can safely be stated to not be an armor because of two reasons. First of all, his body would not have been able to pilot an armor, and the second is because of an item introduced in Phase Shift 1 called the Hi'hirokane. The Hi'hirokane is a sword that's capable of cutting up souls and spiritual beings (such as Terumi). In CF, Terumi takes the Hi'hirokane back from Clavis coffin, because it's the only way to remove Jin from the Susanoo Unit.