u/Glad_Journalist8587

Imagine if "pure vessel" meant not something like "has no desire" but "has no desire other than those inherent to itself".

That is, the only vessel that could contain Radiance (or maybe even face in the dream realm), would be one that would do so if it had no interaction or stimuli that changed their desires or anything similar.

But that would also mean that the King would have to wait for a vessel to do so by itself, instead of instructing it or whatever... maybe.

But what if... he could select a vessel to be a stand-in until one comes?

But also... what if he chooses the vessel that would face the radiance by themselves?

So, as a stand-in, he needed a vessel that would be the least likely to decide to face the radiance on their own,

that is a vessel with

No mind to think.

No will to break.

(and in case they fail, so the Kingdom can be told in a calmer way)

No voice to cry suffering.

It kinda fits but i know it's probably not it. It would make things interesting though.

(this also would not explain why let their bodies be damaged, but hey, if we headcanon already then we can also say that the shades themselves could find a way?)

Along with lore concepts and all that is.