Every trigger user have two bodies: his original flesh body, and the Trion combat body. When he activates his trigger, the flesh body is stored inside the trigger, and is physically replaced by the Trion body.
But Yuma's trigger permanently stored his flesh body (black haired) inside, and he lives with a Trion body (white hair).
In ep. 1 or 2 when he crashes into a car, his face shows a crack (causing Mikumo to become certain Kuga is a neighbor) - the same kind crack Aftokrator's magnetic shard trigger user (forgot his name - the one defeated by Jin in ep.29) shows.
Also when he activates a trigger, he undergoes the same transformation as any trigger user, and have a combat body. Proof is that he seems a bit surprised in Ep.8 when he deactivates his trigger (after the Miwa Squad ambush at the abandoned train station) and his severed arm returns.
So, besides the two bodies (flesh body and Trion combat body), does Yuma Kuga have a third intermediary body from his black trigger?