This comes from a couple of AU gifsets on Tumblr I really loved. Evil Geniuses (or Oswin/Moriarty) was born from this.

In a world where Oswin is not a Dalek, but comes to travel with the Doctor, I imagine him being a bit of a father about his young, fiery companion going off with Jim Moriarty, but letting it happen while she can before the end of Reichenbach, which, as an event that sparked attention, would be accessible by the Doctor at some point.

Rated T only for a not-so-indirect line.

It's not that the Doctor even likes this guy, so why does he keep stopping here, letting his brilliant companion out the doors of his TARDIS, to go have adventures with him?

It's not just because he's a good shag. No, Oswin Oswald is better than that. Too smart for that. Although, the man might be, but he honestly doesn't want to know about that.

She must at least find him attractive, with the amount of flirting they have going on. (She does that with everyone though, really.)

Jim, he's called, calls the TARDIS, requesting her. He reluctantly gives Oswin the phone, and she smiles, flirts, and laughs like this phone conversation is as much fun as any planet in any solar system they've ever visited. His calls are special.

Then, she begs and pleads "Oh Doctor, come on, I must go see him! Just a quick pop to 2011 to see Jim. You like Jim! He's got some technical work on a plan he needs done, and he says I'm the only one who does it right!" As he's stated, no, he doesn't like Jim, but she holds his hand and smiles the entire time she tries to convince him. It doesn't take much before he caves, and off to Earth they go again. ("And no stops on the way. Earth first, then more adventures. I promise, chin boy." She lectures with a pat on his head, like he's a beloved pet.)

When they get there, there stands Jim Moriarty, on a roof or abandoned building or whatever out of the way place he demands the TARDIS land. (He doesn't believe the TARDIS is unnoticeable, no matter what the Doctor's said about the perception filter. He wants to question why Moriarty cares about being noticed.)

"You're late." He says, even though they're in a time machine and no matter what anyone says he flies it just fine.

Oswin rolls her eyes, "Of course we are, Jimboboy."

"Call me that again and I'll put a red sniper dot on you as red as that dress."

"Ooh, so scared, grumpy. Sherl-y got your pants in a twist?" He really should be more worried about why red sniper dots are flirty to her.

Eye-rolling seems to be key in their relationship as well. "Surely, why else would I call you, dear?"

"For a not-so-quick one?" She almost purrs, leaning into Jim's ear, although it's not helping with how much the Doctor can hear. He really doesn't want to know about that.

It's about then he awkwardly interrupts, telling them he'll be back at this spot in a few days time, and to call if she needs him. (He wishes he wouldn't need to include that part, but there was one adventure of their's where he landed and there was a hail of gunfire following the two of them through the doors. "It was just a disagreement!" she claimed, while Jim was more worried about his suit.)

After he's gone on an adventure or two, and is missing her company, he comes back to find a bubbly Oswin unlocking the door and hopping in.

"Have a nice time?"

"Yeah, it was good. Did some work, had some…fun. You?"

"About the same. So, where to next, soufflé girl?"

They slide back into their usual banter, but the Doctor has looked up Jim Moriarty in his time away, and he's not sure if the next time Jim calls, it won't be the last.