How I Built My Villain: Isadora Castor

Mar 20, 2025

Hello and welcome to The Demon Cleaner blog. My name is Nadi Abdi, author of The Demon Cleaner series.

Last week we talked about my heroine, Lillas. Today, we talk about her counterpart, the villain of the story, Isadora Castor. I’m not going to lie. Creating her was easy, especially within the bounds of the community in which they live. I just had to think about my favorite villains and what I liked about them and do that and don’t do things that I dislike about villains.

For one, Izzy exists as an autonomous being. Even without Lillas being Lillas, Izzy is still Izzy. If Lillas didn’t exist, certain events may not have taken place, but we still would have seen the shifts in Izzy’s arc due to her influences. It was important for me to answer the question of “Can this character exist without the heroine?” I needed her to be someone who was there for more than just conflict.

Another thing I wanted to do with this character was show who Lillas would be without her friends and family. Where Lillas exists primarily around mono humans whom she regards as her equals. Izzy exists primarily around other demon knights where there’s a clear hierarchy. These people can’t tell her no. Those close to her can counsel her, but she’s the strongest among them and ultimately her rule is law.

Izzy can be overruled by a stronger demon knight. Lillas is the strongest demon cleaner on the planet. By far. Moving against her is a bold choice, but one people wouldn’t feel so comfortable making if she were more like Izzy and far removed from humanity to the point of only seeing mono humans as a resource.

I can say, with certainty, the situations that Izzy is placed in forces her to show bigger, more dynamic changes as a character than what we see from Lillas. I don’t know that we see much change in Lillas, definitely not in the first book. Meanwhile, Izzy goes through it. The twists and turns of who she can and can’t trust, what she can and can’t do, the grief, and the losses she suffers. None of these take away from the fact that she’s an existential threat to the humans of Guild City, but the lines she’s willing to cross get pushed further and further away until she’s very different from who she was at the beginning of book one.

In fact, the sharp and steep changes in her are what strains her already tentative relationship with Lillas. As the de facto leader of the Guild City knights, and someone who genuinely cares for her people, it was always important to Izzy that she maintain a level of comfort in Knighthouse, offering her fellow knights a reprieve from masking all day in the outside world. That comfort slips the deeper she slides into the Knighthood murder case, a case she should’ve turned over to Command Order and been done with.

After the Knighthood, Izzy is the strongest demon knight in Guild City. It was always a point of contention among the Guidy City knights that Command Order wouldn’t make her a Knight Commander. Not only did she have the power, she had the respect of the knight community, something the Knighthood didn’t have.

Command Order said she wasn’t strong enough, but it’s not like there was a limited number of Knight Commander spots. They just didn’t want her for some reason.

Aside from her natural knight abilities, Izzy turned out to be quite adept at magic, which most knights never learn because they don’t need it. A more powerful knight started teaching her a few things, and she turned out to be a natural, which worked to her strength and her downfall.

A common theme throughout the series is how magic affects spectrals. Magic mixed with their already inherent abilities can often be hard for them to balance. Cleaners use a minimal amount of magic to expel demons and to fight demon knights. Otherwise, even they shy away from it.

That’s why someone like Izzy, who can handle magic, is an amazing show of strength.

Izzy’s ability to forge even a civil relationship with Lillas when every member of the Knighthood failed to do so spoke to her leadership skills, to others spoke to Lillas’s unwillingness to acquiesce to authority and her attempt to sow dissension among the knights.

But whatever anyone thinks of Isadora Castor, she stands as a power on her own. That was the most important part for me during her creation. She doesn’t need Lillas to exist.

That's it for today's Demon Cleaner post. I’m Nadi Abdi. Sign up for the journey. Stay for the drama.

The Demon Cleaner

How I Built My Villain: Isadora Castor

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