I literally wrote a whole fanfic about it, but has that ever stopped me from writing the same meta five times in a row? No. Anyway reading Robin as Grima-influenced/amnesiac Grima adds a whole new layer of tasty to awakening. Robin’s introductory scene, the first thing you learn of Robin, through your eyes no less, is you murdering your best friend. You are, as early as in the prologue, defined as a killer. You are the breath of ruin, the wing of despair. You kill. It’s what you do.
That idea is reinforced through the entire game. You are the strategist, you can seize up people at a glance, you can tell immediately the damages you can do to one another, you can tell which weapon would inflict the heaviest wounds, you are the strategist and your best honed skill is the art of killing people.
That’s not to say you’re a bad person! You do care about others! You can be silly at times! Your supports show that! But the place where you will thrive the most will always be on the battlefield. Throwing flaming ships at enemies, battling inside an active volcano. Hell, that’s even where you bond with others best.
You are the breath of ruin, the wing of despair, and killing is what you do. Better so than Chrom, who begs for you to live, better so than Lucina, who more often than not can’t bring herself to raise her sword against you. You are Robin, Ylisse’s most famed tactician, and you are a killer.
And when the last battle rolls, when Chrom prepares to strike Grima for the last time, you have the option to stop him, you have the option to kill Grima, yourself, with your own two hands. Because you are the breath of ruin, the wing of despair, the end of all things, and you will be yours too. Because you are a good person and you want to save the world, because you love your people and you want to protect them, and the one thing you have ever mastered is killing, and so your only option to end all of this is by turning your only talent against yourself. Because you are Robin, and Grima, and a thousand other names, and killing is what you do.