I'm down to write any sort of Simon tbh! This is a very interesting prompt, and I think it can really give a glimpse into his character, so thank you for sending it in!
I think, at first, he's in denial. Heavily. Everyone else was dead, he had no reason to think you weren't, too. He'd operated under this assumption for years, even when he'd watched from afar as a group buried an empty casket next to the others. He hadn't found you in the massacre, and he hadn't found you at Roba's compound later. Surely those were the only two places you'd be, right? And no one - not the former squadmates who betrayed him, not Roba, not the brass - ever said a word about you being taken somewhere. You were dead, just like the rest. That's the only explanation that made sense. Even in his personnel file, among the list of other names of his former next-of-kin with a "deceased" stamp next to them, your name had a "missing, presumed dead" designation.
But still, part of him never stopped looking. Part of him still kept an eye out whenever he went anywhere, looking for you.
It was a futile endeavor, until one day... it wasn't.
He turns so quickly he develops a crick in his neck later, wild eyes immediately finding yours. He'd been out with the 141 in some dive bar somewhere, buried in between city streets and burnt out neon lights. The rest of the squad quiets, silently watching whatever this is unfold.
No. No no no no no. You were dead. You'd been dead for years. It's why he hadn't spent every waking moment looking for you. The person standing in front of him can't be you.
He stares, wide-eyed and barely breathing. You look different. Of course you do. But he never forgot those eyes of yours.
He could ask the same thing. In fact, he does. He softly says your name, followed by a quiet "thought you were dead".
Right. Sometimes Simon forgets that technically, he's legally dead.
The dam breaks quickly, and Simon isn't sure who moves first between the two of you. You shed some tears, he holds you tighter than he's ever held onto anything in his life. He apologizes for not looking for you, for not doing more to reunite the two of you sooner, but you shut him down. You'd gone into hiding as best as you could after everyone died, never knowing that the men who did it were swiftly dealt with by your older brother. He had nothing to apologize for. And still, he keeps doing so.
Simon fills in the 141 on who you are - his baby sister, the last remaining member of his entire family. Price immediately mentions giving him some leave time in order to "catch up", which Simon takes. Gaz cracks a joke about how you can't be related to Simon - you're way too pretty (Simon is quick to remind the Sargent that he's never even seen his face). Soap, meanwhile, is grilling you about what his LT was like as a scrappy kid, no doubt to find ammo to use later to heckle him about.
