Fitz

He couldn't remember when their names had begun to fit together so seamlessly, or who was the first to call them that. All he knew was that there was a chance – a very good chance – that tomorrow, the name would never have the same meaning again.

Fitzsimmons.

No, if they couldn't fix this, there would be no Fitzsimmons. There would only be Fitz…too short a name, always waiting for the better half, the half that made them complete, that made them Fitzsimmons.

As he stood there, separated from her by glass thin enough to hear through, he wondered how long it would take for people from Fury down to Skye to break the habit of the name Fitzsimmons, and how much it would hurt, if he would never again have her answer echo his, never feel the brush of her ponytail on his shoulder as she turned her head just a bit ahead out of sync with him, only then to see the reaction of whoever was addressing him (them) when they realised that there was no Fitzsimmons.

Even if they could cease with the name right away, Leo was sure, he would always stop for a beat, expecting the two extra syllables to follow. How much would it hurt, when he would have to realise they would never come?

It wasn't just their joined name that would remain incomplete. His sentences, too, would forever be hanging, waiting for Jemma to break in excitedly to finish them. Who would meet his overexcited, gushing theory when faced with a new piece of alien tech? Who could? On this plane, perhaps on this entire planet, there was only her.

Could he ever sound excited again, when it would be that alien tech which excited them both, that took – was taking – takes (he didn't know the tense anymore) her away?

The truth was, as pathetic as it sounded, as bordering on unhealthy as it was, he no longer knew how to be just Fitz. He stared as she broke eye contact and turned away, retreating into the lab again. She looked so very small, so very lonely in the middle of all their genius. Most of the things in that lab were their lives' work. Theirs. Theirs. It was always theirs. Jemma and Leo. Fitz and Simmons. Fitzsimmons.

How small and lonely would Fitz feel then, to be in that lab alone, a space which would be too empty and too silent without her? He didn't think he knew how to work anymore, without maneuvering around her lab rats and decaying things-unknown. Just imagining it now overwhelmed him with how excruciatingly unbearable it would be, if the silence of the lab were to press in on him from all sides, unbroken by her occasional giddy exclamations of progress or absent-minded humming.

"You have to fix this," he told her, because it was true. She was the only person capable of fixing this, and he would believe that. He would believe that because the alternative was impossible.

"There's no one to create an anti-serum from, except…"

Their eyes met, distorted through the haze of tears and the glass door, and like so many moments of their lives together before, understanding sparked off them both and kindled in their hearts. It started muted this time, because, for a moment, neither of them dared to think that they had found their answer. Yet as always, the spark built into a flame as science gave them what they had always depended on it to give: explanation, logic, sense and understanding, all gathering into a roaring hope.

He didn't think he remembered the dash up the stairs to grab the box with the helmet. He only knew that a moment later, he was in the lab again, looking at her, both standing beside their next puzzle to solve.

It was as it should be. This was where he belonged, not sitting helpless outside with his back against hers through a glass door, the two of them trying to solve two halves of the same puzzle separately. This was their domain, their mystery to crack, their problem to solve.

Theirs, always theirs.

And they would fix this, the way they always do everything.

Together.