Nicole
"But, Tori, you can't keep me here forever."
"Oh, but there, my dear sister, is where you've got it wrong." The Doctor frowned. "You're 180 years old and my only sister, and you've got to stay in this room! And don't call me Tori," he added.
"The DOCTOR travels alone, the DOCTOR hasn't any friends, that's what everyone thinks because they don't know I exist! I barely even know I exist, what with the TARDIS making new rooms all the time. You've got all these friends, and I haven't anyone but you! And I'll call you what I want!" A teenage-looking girl with long black hair and green eyes looked at him reproachfully.
"Now, Nicole…"
"Don't you 'now, Nicole' me becausethat won't work this time, sir! I'm tired of being stuck in this blue box with no company!" Nicole swung her hair over her shoulder and faced away from the Doctor, sulking.
"The last time I let someone see you, they almost died!"
"I was only 10! A baby!"
"All the same." He pointed a finger at her. "Nicole, you know why you can't leave. You're special. The last Time Lady."
"So that's why you're telling everyone you're the 'last of the Time Lords'? 'Cuz you've got me?"
"Of course!"
"Well… I don't like the look of that Rose girl you've picked up. She's almost gone and went into my studio. Only, I had it locked."
"Oh… That was the locked door… But you shut up about Rose. She's fantastic, and she's going to stay as long as she wants."
"If Rose doesn't want to come any more, will you take me somewhere?"
"Well… where?"
"I want to go to Gallifrey!" Nicole grinned, and clasped her hands together. "Please? I promise I won't do anything bad for a hundred years, just please can we go to Gallifrey?"
The Doctor looked at her smiling face and couldn't bear to crush her dreams.
"Why go to sad old Gallifrey? I'll take you to see the Sapphire Waterfall on Midnight! Wouldn't you like that?"
"Anywhere, Doctor! Just take me somewhere!"
"I'll do it, but you have to promise you won't do anything to Rose. Maybe I can convince her to stay home for a day or two, then we can go."
"All right then!"
"I'll see you later, Nicole."
"Bye, Doctor."
Nicole shut the door and retreated back into her studio. Today she was painting the TARDIS.
The Doctor leaned against the wooden door and sighed. One day she'd have to know. Know that Gallifrey didn't exist. As the last of the Time Ladies, she alone had the power to travel between universes without ripping holes in the fabric of time and space. He never wanted her to find that out.
If he ever died, there was nothing stopping the daleks from harnessing her power and wreaking havoc across multiple universes. There would be no one opposing them.
No one could ever know about her. He just couldn't risk his only family.