system
Given the following post, respond as if you're commenting on Reddit:
human
[evil dead] what makes ash “unpossessable

What makes ash “unpossessable”

Or can he be possessed?

Im not sure he is either very lucky (sunlight purifying him) or very powerful (chopped his hand off) but even then

Why didnt the sun purify citizen deadites that were in the sun?
gpt
It's mostly Ash being a sort of Chosen One. Whether being the chosen one adds an extra layer of resistance on top of his will power or he's the chosen one simply because of his will power is unknown. But the sun did help.

The first one hit him the hardest, because he was not only blindsided by it, but also because he hadn't quite "snapped," yet. But deadites are shown to largely, if not exclusively, function in the dark. So its certainly possible sunlight is some sort of bane to them. In Ash's case, it was enough for him to fight back and subdue the darkness within him.

After that, the darkness around him tried to torment him. Not only out of fun, but to break his will. When he wasn't breaking the way it would like, it concentrated itself in his hand, in an effort to kill him and take over his corpse. This backfired, as after finally snapping, his will was as strong as ever.

After that, it was established that although the darkness may be able to affect his body (such as growing an evil twin from him), it's not powerful enough to ever take full control of him. And anything the darkness does to affect his body clearly hasn't been worth the effort.