Superhero Verse Celia and Alix

She's the first villain I've made for my heroesverse(I need something to call this storyline) she's really just a minor villain though and not very powerful.
Her power is invisibility, she's able to turn herself and the clothing on her invisible.
I decided to make her a villain because I was looking at her design and was like, "wow, she is super boring looking, I don't much care for her design at all" Every time I looked at her I'd think of this vine www.youtube.com/watch?v=vvMF6b… She does look like a "chURch GirL who GoEs to ChurCh, and ReaDS HEr BiBle" She just looks like a very polite young lady, who is very nice and makes good grades in school and never gets in trouble. But then I also started thinking, "she looks kinda shifty, she's got her hands behind her back sort of like she's hiding something" She kind of looks like she's on the verge of snapping.
So I started coming up with a character for her. In public, in school, and around every one she knows, she is super nice, a little annoyingly so. She makes perfect grades, she had quite a few friends, and is fairly popular. She never gets in trouble, always does as she's told. She seems perfect, just an all around great person.
BUT, nobody knows she's pretty much a complete psychopath, everything people think she is is all just an act. Nobody knows about her powers. She sneaks away at night and commits murders as the villain [insert name here] She's a serial killer responsible for a whole string of murders, nobody has ever seen her, due to her powers of invisibility. I didn't really come up for a reason for the way she is, I'm not sure if I want to, I kind of want her to be the type of villain who is irredeemable. Just absolutely insane and feels no remorse.

The only person she actually somewhat cares about is (whatever this dudes name is) They have been best friends for years. He is a bit shy and awkward, but a genuinely kind person, he doesn't do the best in school, but he tries his best. He wants to help people, and tries to be friendly to everyone he meets. He doesn't have any powers. He doesn't know about who she really is. But he is the one who ends up piecing together that she's the one responsible for the murders, and catches her in the act. He's heartbroken and drama ensues.

These two don't have much connection to the other heroes I've designed, they exist in the same universe in the same town as many of them, but their story line is sort of separate. Their whole thing would be like a mystery arc that mostly takes place at their school.