"Shiryo" translates from Japanese to "souls of the dead". While it makes sense since Revenant and the Eidolons are technically just that, but you also have to remember that they are quite literally "revenants", as in they are beings that have come back from the dead for revenge.

So instead of the current name, why not use "Onryo" (meaning vengeful spirit) instead? They are described as ghosts of revenge, meant to cause harm against the land of the living. It would fit more into Revenant's general theme, and would probably fit more to the general look of the helmet (because of the Oni-like horns).