My novel is about women supporting each other through trials and tribulations (character transformation) while at the same we watch a deviant (in parallel) intruding upon their lives. Their transformation is positive, while his escalates over the years to become that of a serial killer. I haven't been able to classify it because I can't find anything that resembles the concept. I juxtapose their innocence and positive transition with his evil and negativity. The protagonist and antagonist interact in the beginning of the novel and the end but their lives are entwined throughout without either realizing it. I'd like to know what genre I can use when speaking about it.
Typically, any book that features a killer would be a thriller or a crime novel.
Thrillers are characterized and defined by the moods they elicit, giving viewers heightened feelings of suspense, excitement, surprise, anticipation and anxiety
Crime fiction is a literary genre that fictionalises crimes, their detection, criminals, and their motives.
I don't think the fact that you're focusing on character development is enough to entirely remove it from this categories. I might go with "literary thriller" or "upmarket crime novel" as your final descriptors.
Literary fiction is a term used in the book-trade to distinguish novels that are regarded as having literary merit.
Upmarket: When agents and editors talk about “upmarket” fiction, they are referring to books that appeal to both audiences. They are books that have excellent writing along with a story line that appeals to a mainstream market.
Stories that illustrate ethical concepts through the actions of characters are called parables. https://en.wikipedia.org/wiki/Parable
A parable often involves a character who faces a moral dilemma or one who makes a bad decision and then suffers the unintended consequences. Although the meaning of a parable is often not explicitly stated, it is not intended to be hidden or secret but to be quite straightforward and obvious.
The defining characteristic of the parable is the presence of a subtext suggesting how a person should behave or what he should believe. Aside from providing guidance and suggestions for proper conduct in one's life, parables frequently use metaphorical language which allows people to more easily discuss difficult or complex ideas. Parables express an abstract argument by means of using a concrete narrative which is easily understood.