slow burn and enemy to lover, sign me up!

Where did you see him fight back ? My boy said he's never bottoming again for Enzo, yet here he is doing exactly that cause he's scared for his life. If anything, this scene reads more like coercion, because Rian's choices are being shaped by fear rather than genuine freedom to refuse.
People are mistaking attitude for agency. Rian can be confident, sarcastic, and talk back all he wants, but where's the actual resistance ? He set a boundary, Enzo pushed past it, and Rian complied because he's under duress.

To be fair, Rian's the type who's so shameless that he'd back down when driven into a corner and wag his tail like a dog, pretending to be loyal, but anytime he's given a chance he'd bite and run away. He knows that fighting head on is only gonna incur losses.

Being cowardly is okay when you can survive –Rian, probably.

Btw, I get reminded of "Assorted Wilderness" because of their dynamics. "Caste Heaven" is another one that I liked because the uke never backed down.

What I mean is that he never just goes along with what Enzo says and follows him blindly without his own agenda in mind, he knew what Enzo was capable of and was actually thinking smarter of the situation he is in. It would be dumb to physically fight when you are fighting 1 to many opponents, but he is never afraid to speak against Enzo. They could've written him being scared of Enzo and following his demands all the time, but did Rian even follow it thoroughly? Who says you have to physically fight? Rian has his own plan against Enzo, even if right now he is complying under duress. But all I mentioned in my comment is his character and personality, we don't know what Rian or Enzo is going to be like in the next couple of chapters anyway.