This will probably develop into a story with a few parts.
A Madman in a Box
"One day, you'll see!" cried the young boy excitedly. He leapt to his feet and pointed at the two suns of Gallifrey shining down on them. "I'll be out there among the stars, seeing all of time and space, all of history. I'll be making history!"
The older girl smiled at her friend's enthusiasm, though she knew how silly it was.
"You know you can't do that. We aren't supposed to change history, it wouldn't be right. It's better to just observe from afar. Don't get so invested in things!"
He turned to her with a brightness in his eyes, and an incredulous smile.
"How can you say that? To see everything out there... what could be better?" The girl merely pursed her lips. "Besides, isn't it wrong, to just sit here and do nothing while there is pain and suffering that we can easily avoid?"
"What, are you going to go fix the universe?" she asked sarcastically, though her tone was gentle. "Change every moment in history where something has gone wrong?"
The boy just grinned.
"Moment by moment." His friend shook her head disapprovingly, but she couldn't help the smile that forced its way to her lips. She was amazed and delighted by the eager way he spoke about travelling, the confidence in his quirky grin, and his inherent desire to help others.
"Well you can't fly around in the stars without a TARDIS," she pointed out.
"So I'll get one!" he exclaimed.
"The High Council will never give you one if you're going to misuse it like that!"
"So I'll steal one," he said with a sassy wink.
"Oh wipe that cheeky grin off your face," she teased. Grabbing his sleeve, she yanked him back onto the ground with her.
"So you'll just roam the universe, all alone in your TARDIS, slaying dragons forever?"
"And do you know what that'll make you?"
"A hero? A knight? A protector of worlds?" he supplied proudly.
"A madman in a box."
The little boy made a face at his companion as she laughed, snorting in amusement.
"Well at least I don't snort like a pig," he teased her.
"Oh, pig am I?" The boy stuck his tongue out at her. With a playful yell, the girl lunged over and tackled him. Locked in a friendly tussle, the boy and girl shrieked as they began to tumble down the hill. After a moment they erupted in whoops of laughter as they rolled rapidly over the red grass.
With an 'umf' the friends hit the bottom of the hill and stopped abruptly, the girl landing on top of the boy. As the boy groaned beneath her, the girl pushed herself up so she was hovering above him.
Without any warning she leaned down and gave him a quick kiss. Stunned into silence, and blushing madly, the boy lay still as she jumped to her feet. Standing up timidly, the boy was embarrassed to feel the color in his cheeks.
"What was that?" he asked shyly, his hand shaking as he brushed his floppy hair out of his eyes.
"Well," she said confidently, "I figure that someday when you're out there traveling you'll be quite a Casanova, so I wanted to be able to say that I was the first to kiss you, before all those other girls get their hands on you."
Though he was still blushing, the boy smiled in surprise.
"Did you just say Casanova?"
"I have picked up some human cultural references over the years. I spend too much time with you, you human-lover," she mocked. The boy grinned, his familiar enthusiasm returning to his face.
"How could you not be interested in them? A race that looks just like us. Completely technologically inferior of course, but that's what makes them all the more interesting!"
"Just like I said, when girls see that look on your face, they won't be able to help falling in love with you. You really will be a Casanova," teased the girl, captivated by his bright eyes once again. The boy waved away her words, not seeming to understand the implication behind it.
"I don't want to be a Casanova. I want to be a Romeo!"
"Romeo! From Shakespeare's 'Romeo and Juliet'," recited the boy. "Romeo and Juliet are the ultimate symbols of true love."
"So you want to just have one true love?" the girl checked. He nodded emphatically.
"Someday I'll have one," he said confidently, looking out at the sky once more. "I'll find her out there somewhere, I'm sure of it."
The girl felt somewhat sad at his proclamation, though she told herself it was silly. She was only eighty-six years old, and he only seventy! It was silly to think that her crush meant anything special. Besides, she could never travel as he wanted to do. Gallifrey was her home, how could she leave it? The rolling hills, the red grass, the singing mountains: those were all she needed.
"Well you'll have to come back and visit every once in a while," the girl said. "I'll want to know all about those worlds that you explore."
"Why don't you come with me?" he suggested passionately. "We could travel together! Wouldn't that be fantastic?" A dreadful feeling filled her heart simply at considering the possibility.
"No, I could never do that," she answered truthfully.
"You can do anything you want," he said with a smile. "And you never know, what you want might change. Maybe someday we will be travelling the universe together."
"I doubt that. If we did, do you know what that would make me?"
"What?" he asked.
"A companion to a madman in a box."