I want to talk about tempering

[Remedi]

I always saw tempering as being similar to Mass Effect's indoctrination. Once you're indoctrinated, that's pretty much it. It's irreversible. People who have been indoctrinated, unfortunately, have to be killed. Because it goes way beyond mind control. Indoctrination (and tempering) actually alters your entire being. It's mental, physical, and spiritual. In the ME series, only the Leviathans, the progenitors of the Reapers, can release someone from a Reaper's indoctrination.

It is quite possible, that the Warrior of Light will learn how to reverse tempering in time. We still don't know the extent of the WoL's powers.

Note that both Nael and Lousoix had the grip of the primal relinquished off them, The canonicity of that might be questionable but I believe that the effect of tempering can be removed