Plague

Steah

So why is Plague trying to kill survivors? No where in her lore was she a killer,. Why did the entity take her?

Lexilogo

It appears as if the explanation is Plague's faith- She prayed, and a god DID answer her. That's enough for her to do what the god wants, even if it involves horrific ritual murder and sacrifice. She was probably more reluctant when she started but she's had a lot of time to have her mind steadily hollowed out by all the slaughter.

Though, my personal headcanon is that the Entity doesn't actually consider Adiris the "Killer" and simply considers her the host for the disease, which it considers the actual being that's been given the title of "Killer" in the trials. Adiris is convenient but the killer is The Plague, not The Priestess.

brubli

she's just doing her job as a devout priestess and pleasing her god