It could be part of it, I figured the whole thing in general might start spitting out dark spirits, combined with the slimy stuff taking over some people or at least getting them stuck like a tar pit would. 

As far as who the hero is and who the victim is does not matter to me, but I can also see how it might be more appropriate if Avani is the one, given prior situations and such. Do we want thing fight to result in no survivors other than Avani and Kasai or do we want to leave at least one or two stragglers? Personally I think no other survivors offers more for the 1x1 character development (having no one else to blame/no one else who experienced the same thing/savior-saved complex), while on the other hand one companion could also provide "background noise" after the fact. However, I would choose the former.