Is there a canon moment where Merikh starts to fall for MC?
There is no single moment, rather a culmination of moments. And I think that goes for all characters.
There is also the falling in love part of the story and the being in love part of the story. There is a moment where, depending on your choices, Merikh will admit to himself and possibly the MC that he's falling. But there is another point in the story where Merikh allows himself to go all in.
Merikh doesn't fall in love, as much as he gets jumped by it. It creeps up on him and scares the living daylights out of him and then he tries to run from it.
(If I had to narrow down a moment when he realized that he isn't just superficially attracted to the MC is during the hunt.)












