Will is the Protagonist as the story is told through his perspective including several key flashbacks.
There is the Cult Quartet: David, Eden, Sadie, and Pruitt. They’re all Tricksters whose deadly plan doesn’t become clear until the end of Act II when they each don Nemesis ‘masks’.
Kira is an Attractor figure to Will. He is trying to deal with the grief of having lost a son, just as Eden is in her own demented way. If we were to look at this story from a macro perspective, one way to think of it is Will goes through all of this shit in order to break down his psychological defenses and — if he can recuperate from the madness of this deadly event — enable him to make an authentic connection with Kira. The fact they go through this chaos together and have to rely on each other to survive, suggests perhaps they will end up together. Or one or the other go mad from the bat shit crazy stuff which just transpired.
As I discussed and Hay and Manfredi, the screenwriters of “The Invitation”, the script provides a Will scene with each of the other characters, one on one. It’s a great way to allow each of the characters to explore a unique aspect of Will’s psyche and where he is in his journey into and through paranoia.
Oh, and this: If you watch the movie, they do NOT show Claire’s battered body behind the house, the last we see of her is Pruitt going outside to move his car so she can leave. It’s even more sinister because we don’t know, but can figure, he dispatched.
Pruitt is one whacked out dude. And Sadie is even more bizarre!