The corruption I'm talking about is something that, like it's name, "corrupts" the employees. Interacting with "ghost stories" or "darkness" can corrupt a person (although in varying amounts). It can possibly manifest as physical in which this other person doesn't look human anymore or it maybe mental (often, it's both). An example of mental corruption (another novel spoiler) would be something like Kim Soleum growing fonder of Braun and thinking that they're "genuinely friends". An uncorrupted Kim Soleum would not think that as he is a rational coward that knows that Braun is a terrifying non-human that could kill him if Braun simply wishes so. Of course, that's just one of the most subtle example of a mental corruption.

I wish they would show soleum's corruption in a subtle way! Kinda like in the novel; that part was sooooo perfectly done ╥ ╥,,, I didn't even knew he was corrupted at the beginning!