So let me get this relatively straight...

Nitya and Argun were in an abusive relationship. She decides to leave to the Carcosa Echeloen program in which an ancient alien species decided to terrafotm the humans into the monsters you fight along the way in each biome while Arjun can't accept his own mistakes and will keep moving forward no matter the consequences.

All the while Nitya becomes a monster too and has a rebellion with the other leader king monster and takes over and creates the constant a barrier which is a metaphor for her trying to escape her relationship with Arjun. Side not she also meets some other chick and starts to have feelings for her but sounds like she was killed or something else?

I am yet to get the final tree cut scene but that has something to do with Arjun mate Sebastian either being killed or some crap going down?

I don't mind any spoilers now as this is not something I'm emotionally invested in like I was with Returnal.