The fact Kirin males have small muzzles and soft features implies these traits were sexually selected for. It's not clear where Kirin came from, but it's an extremely safe guess that whatever came before Kirin had the "males are taller and tougher" setup that the vast majority of mammals and animals in general have.

But Kirin males are soft-looking. Not any taller. Meeker in temperament. This would NOT evolve unless being girly-looking was an advantage for male Kirin. The Kirin species would not just spontaneously lose masculine males for no good reason. The ONLY plausible way you would get from typical macho males to softboi males that are so common literally the entire male population of the Kirin species is soft-featured......is if female Kirin sexually selected for this, on purpose. At some point in their evolutionary history, female Kirin would look to their left, see a handsome manly boi, look to their right and see a cuter soft boy, and the females would all need to consistently select demure males such that those genes became widely propogated.

TLDR: Kirin girls are biologically wired to prefer twinks and submissive males. Presumably, there is some direct reason (or several) as to why they have this preference, for it to be wired in them. but i gotta go to bed so I'll leave that to you to figure out.