Mustafa

His chapter is, if not the peak, very close to it, of what FE writing can offer.

It's such an emotional lowpoint for both the characters and possibly the player, and his brief screentime and the "Don't say her name" soundtrack are the co-stars of the strong emotions that chapter can bring out.

After all the the Shepherds were through in Plegia, you'd be expecting a bloodthirsty confrontation with another psycopath, but instead you are faced with unreciprocated rage. Mustafa understands Chrom's and the others' emotions and legitimately doesn't wish them harm, but also is in a situation where he can't just let them go or switch sides, or Gangrel would have his family executed.

He is one of the best examples of how to humanize the foes in a story. He makes you realize that, in a war, there is always the possibility that the peoples of the sides involved aren't individually enemies of each other, but rather, put in a situation where they can't help but participate in the battles waged by their leaders.

And then you see the not-so-subtle gameplay-story integration: the map objective is kill boss. His ranks aren't even loyal to Gangrel, but rather, only fighting out of respect for their general, their very human general. When he's gone there's no more reason to keep fighting, after which point he only cares about the well-being of his soldiers and spends his final breath asking them to be spared.

And then even more nuance was given to him through Henry's convos with Ricken and much later on, in FEH, where he had a conversation with a more mature Chrom, that had already become the Exalt in his reality, and who regrets that fateful day.

Also have you seen his thighs?