First of all, Kat is a badass fighter. When the MC "harasses" her, she doesn't react, just keeps talking aggressively but doesn't resist, and is all wet and almost immediately has an orgasm. She has a huge crush on him/her. Need more updates to find out what is going on in Kat's mind, looks like she is into bondage and submission (or just hatefuck).
There is not much difference in the dialogue between the FMC and the MC, only the dick... and you have the option to cum inside or make them swallow =)