Anything in the Universe
Set towards the end of season 4. This is different from the others, as Rose is only mentioned in a conversation between the Doctor and Donna.
The Doctor
We're close to the Andromeda Nebula. The TARDIS is just hovering in mid-air (well, mid-no-air), and Donna and I are sitting on the floor, looking out.
"It's beautiful," Donna says after a while. "All those colors…"
"Yup," I agree.
"Looks like fairy dust, don't you think?" Donna says dreamily. "As if I could reach out and grab a handful, and wish for anything I like…"
"Don't go there, Donna," I interrupt her. "Fairies aren't the lovely, magical, sweet little angels that humans think the are. They're nasty and greedy, and they certainly don't grant you any wishes."
Donna looks at me. "You're not tellin' me that fairies actually exist, are you? Blimey!"
I look at her, startled. "Of course they exist. Didn't you know?"
Donna only rolls her eyes in response.
"What?" I ask her, not understanding what I did wrong.
Donna shakes her head, indicating, she won't discuss this. Fine. I look out into the vastness of the universe.
After a while, Donna speaks again, and what she says startles me.
"If you could wish for something, anything in the universe, no matter what it was, what would it be?" She turns to look at me. "Would you wish for Gallifrey to be restored? For the time lords to return?"
I'm so surprised that it takes me a while to find my words. I'm about to answer, yes, of course, but then I hesitate. Is this really my greatest wish in the world?
"They've been gone too long," I say slowly. "They're little more than a memory to me. The TARDIS is my home now, and my companions are my family."
"But there must be something… something you long for more than anything else," Donna insists. "And if you could make that one wish, you could have it back."
Oh, yes, there is.
"Not something, Donna," I say softly. "Not something."
"Someone, then," Donna says impatiently. But then she casts me a sideways glance and notices my face, which has become stone cold and frozen. My pain is showing clearly, I'm certain of that. And she understands, of course she does. She reaches out her hand and puts it over mine. "Someone you lost, and whom you've been missing ever since. Someone you can't forget. Doctor, if you could wish for Rose to come back, wouldn't you?"
I would certainly want to wish for that.
"I don't know," I say out loud. I don't really like where this conversation is going. It's all too hypothetical, and what good are dreams and wishes, if they won't ever come true? But to humor Donna, I think about my answer. "I'm not sure if I should use that one wish for myself, you know," I say eventually. "If I could wish for virtually anything… shouldn't I think about it carefully? Make a wish for the good of the whole universe?"
Donna all but cuts across me. "The universe has you. Whenever there's trouble, you're there to save the day." She squeezes my hand. "But you need motivation, Doctor. You need something to hold on to in order to muster the will to go on doing what you're doing. You need more happiness. No one deserves happiness more than you."
"But I am happy," I protest. "I have the TARDIS, and I have you, Donna Noble, and you're brilliant."
Donna smiles, but then she shakes her head. "I think that you would only be happy – really, really happy – if Rose were with you once again."
She's right, she's so right. Without Rose, it's as if a part of me is missing. No matter how happy I feel when I'm on the hunt with Donna – it's got nothing to do with how happy I actually am.
"Maybe I would," I admit, answering Donna's question. "But still I couldn't do that – make a wish for myself if it was in my power to make the whole universe a better place. I just couldn't."
A mischievous glint appears in Donna's eyes, but only to be replaced by something between affection and compassion. She covers my hand in hers again. "If you refused to wish for Rose to return to you, even though you want it more than anything else in the world, then I would make that wish for you."
A/N: I wrote this a couple of weeks ago, just after "Turn Left" aired. Funny, though, that Donna actually did turn out to be responsible for reuniting the Doctor and Rose for good.