Strengthening the soul would require a completely different approach.
Since the concept of souls itself was different, this was natural.
An Awakened cultivated their affinity to become stronger—the Supernatural race has varying methods to become stronger, unique to only their own race, so it came as natural for the soul to demand another method to strengthen it.
Iris was foreign to the concept.
She has never come across the need to strengthen her soul in any way.
Because of that, she doesn't know what Rex was trying to gain by going through with this.
He even made a deal with Elder Tilirith, a hostile force.
Mavenna should know something about this, but Iris has no intention of asking her, she was too focused on Elder Tilrith. She didn't trust the Demons at all much less the Demon Queen, she knew how barbaric the Demon race was.
If Elder Tilrith did even remotely try to do something bad, she would intervene.
