I can't seem to understand how to get memories of Kanathar everytime I meet him he just fights and I can't seem to be able to tell him about nyx can y'all help?
You can tell him about Nyx after you visit the manor. He'll show up automatically when you enter the monolith. The different endings is if you win against his fight or lose against him.
The Power word achievement will be done automatically after you get the losing ending and then meet him again in another cycle.