Even after discussing it with her a dozen times, even after she's made herself clear, Chrom still can't fully accept her choice.
It hasn't been an easy one. At times, Robin wanted to be selfish, wanted to promise not to sacrifice herself and stay with her family and best friends. It's not just Chrom who would be devastated, or the children either. Sumia and Lissa, who are like sisters to her. Ricken, who's just like a little brother. Sully, her training partner. Nowi, who's lost more than enough people in her thousand-year lifetime.
She wants to be selfish. She wants to stay with them and let future generations deal with Grima when the time came. But she knows she can't; Grima's done enough damage as it is and the only way to ensure the best future one-hundred percent is to end him by his own hand. Her hand.
When the time comes, Chrom offers yet again to land the last blow, but she pushes past him, sword in hand, and drives the blade straight into her own heart. You and I will never be one and the same, because I'll never let any harm come to the people I care about!
"Robin!" The first cry comes from Lissa, and it makes her wince. Others gasp, too, calling out for her in disbelief. But none sound more desperate and broken than her husband's as he rushes forward, trying to embrace her disappearing body. Robin, no, Gods, don't leave me, don't leave us, please, Robin-!
She can't take it. This is hard enough for her and the last thing she needs is to imagine him suffering, especially when she knows he's stronger than this. So she reaches out and tweaks his nose with as much strength as she can muster.
"Stop that," she scolds gently, her own voice sounding miles away by now. "No crying. I want the last thing I see to be your smile, okay?" He tries to protest, but she tweaks again with now-transparent fingers, and he relents.
"No crying," he agrees. "But we're going to miss you, you know."
"We'll meet again in a better life," she promises. Everything and everyone before her are shadows and the clearest thing she can see before it all fades into darkness is Chrom's smile.
-x-
Her hairbows and her wedding ring lie on the ground next to her robe. Chrom musters the brightest smile he can and goes to retrieve them, pressing a bow into Lucina's hand and then Morgan's. He can see the tears gathering in Morgan's eyes and Lucina's solemn expression.
"No crying," he tells them. "She'll be back again. And we'll be there to welcome her home."
"Anything can change," Lucina whispers, echoing his oft-spoken words. Morgan tries to smile as they both hug him, and Chrom closes his eyes, taking comfort in their closeness.
Robin. She wasn't perfect by a long shot. She was flighty and immature and awkward, she'd thrown things at him over her own mistake, she was better with books than she was with people. But underneath all that immaturity was a good heart, someone who tried her best.
No more being selfish, he decides. It hadn't been any easier for her to sacrifice herself than it had been for them to let her go. She'd throw rocks and soap at him forever if she came back and found out he'd spent all his time weeping over her.
That night he puts her wedding ring on a silk cord and hangs it from the hook on her dressing table's mirror. He can still see her smile in the mirror next to him, and he knows it's a good sign.
-x-
She doesn't know how much time has passed when she wakes up in the same field they found her in long ago, but the first thing he does is pinch her nose just like she'd done to him.
"Hey!" She gives him a dirty look, just like when he'd accused her of not being a lady. "I just woke up, what's the big idea?"
"I owed you that."
He helps her stand, and she sees the back of her hand is bare. Grima's mark. It's... And then she remembers, the last time she'd seen him they were on Grima's back. Her sword in hand, him crying out for her, her transparent fingers against his face.
"It's all over now," he says, wrapping his arm and his cloak around her. "Welcome home."
She can't help but laugh as she throws her arms around both him and Lissa. Their eyes are full of happy tears and she feels a few welling in her own. It's over. It's really over. And I'm here.
"Looks like this time I got to keep my promise."
Author's note: Yeah, I know these Chrom/Robin sacrifice ending fics are a dime a dozen nowadays, but I just had to write my own take on it. Someone suggested Robin would tweak Chrom's nose if he started weeping over her sacrifice, and I can really see it. She'd never want him to be sad after all the good times they had together, and even if she never came back she'd hate to think of him mourning her forever.