Maybe this is me showing my age, but your story put me strongly in mind of the classic Warhammer character Aekold Helbrass, who inverts the 'traditional' imagery of good and evil by being a champion of darkness whose steps bloom with flowers and new growth. I liked your exploration of the psychology of a Plague Brother here. The contrast between the two different perspectives of the Havoc warriors, and between the narrator and the Battle Sister, worked well with the theme: I saw it as exploring the idea that no-one, not even a Plague Brother, sees themselves as "Evil" and their actions as "wrong". The work was a little choppy grammatically at times, and I encourage you to be careful with your punctuation to maximize your readers' engagement. I did like the detached style of the narrative as it worked well to give me a feel for the narrator's personality.