There are many reason why I think Rey is a Skywalker, or even Luke's daughter, not the least of which is that only when Rey arrives on D'Qar, does Artoo-Detoo wake up and show the map. He's been given strict orders to wait until she comes, to reveal all, and so he does.
Master Luke said it would be a long wait, and so did Artoo-Detoo knew it would be true.
His memory banks played back the last meeting they had. He had sent Artoo away, off to Mistress Leia and See-Threepio, and then, he disappeared. Ever since, she had been searching for him. Knowing Artoo had been with him, she had implored the little droid, asking if he had known where Luke had gone. But Artoo had not answered. Next, Threepio demanded Artoo tell them. Instead, that had been when he had shut down for good. Or, at least, shut down to low power mode.
After all, he was just being a good little droid, following the commands he had been given by Master Luke. He always was that. Really. No matter what Threepio thought, Artoo had always followed directives, as given to him by Master Luke or Mistress Leia, Master Bail or Master Obi-Wan, Mistress Padme or Master Anakin.
And now, that directive had been to wait. And so, Artoo had, in a state that, if he were organic, could have been called sleeping with one eye open.
No matter where he was, his scanners were operational, search for the thing that Master Luke had told him to be on the lookout for. It was a code, uploaded to his matrix by Master Luke. He didn't know what the code was for exactly, just that it was important and Artoo was to keep his sensors attune to it.
For so many years, after his shut down and after Mistress Leia had left politics, he had been placed in a storage space in the bunker where the Resistance had established themselves. Frequently, a tarp was draped over him, trying to prevent oxidation from corroding his circuits. Threepio tended to him, surveying any wear and tear that may have occurred. He talk to him during those visits. At first, he reprimanded Artoo for seeming to be stubborn, not divulging any information Master Luke had imparted to him. Then, Threepio began begging him to wake up, return to them, for the simple reason that the golden protocol droid missed his partner of these last thirty years.
Of course, Artoo knew the truth, that they had been partners for much more than that. But that information may overload Threepio's circuits. So, he remained quiet.
Eventually, there had been a development that intrigued Artoo. It was the presence of a newer-model BeeBee unit. Whenever he was planetside, the little droid (one smaller that Artoo, at long last!) would come and visit, chatter to him, try to bring him back to a functional state. Artoo would sift through his memory banks, comparing his younger self to the newbie. Artoo came to believe that if the worst happened, if time took too much of a toll on him, at least Threepio wouldn't be alone.
Even Artoo was beginning to think the time would never come.
One day, Threepio came to Artoo, fretting more than he normally did. It seemed that Threepio had failed to activate the long-range tracker on the Beebee unit. Now, the droid was lost on a mission of vital importance, somewhere on the planet Jakku. The designation triggered something in Artoo-not enough to bring him out of his current state, but enough to put him on alert.
For Jakku was something important, something to do with Master Luke…
Now, the astromech droid panicked. He knew this was information was vital...but he could not remember why.
Now, in silence, Artoo replayed a scene buried deep inside him trying to remember Jakku. There was Master Luke, Master Han...and a girl. On a desert planet, but...not Tatooine. No, he had heard Master Luke tell Master Han. "It's too dangerous to go to Tatooine. It's a known part of our history, of mine and my father. It's not safe."
"It was never safe, kid," the smuggler reminded the Jedi Master.
Luke smiled, ruefully. "It's less safe than it ever was," he amended. "No, It needs to be somewhere else."
Han looked behind where Luke was standing, behind where Artoo had parked himself. "Are you sure you can even do this? I mean, I can't even fathom this, even if my son…"
Luke's gaze followed Han's, his tone growing sadder by the moment. "It's what must be done. This is little different than the decisions made by Obi-Wan, Yoda and Bail Organa about Leia and I, after the rise of the Empire and Darth Vader." Then he looked back at his friend. "The Force guided Leia and I, brought us together when it was needed. I believe it will guide her too. And she will save Ben."
Artoo noted Master Han's expression, the incredulity that always seemed etched in his face, when Master Luke spoke of the Force. "And you're sure he's there, this Lor San Tekka? He's agreed to all this?"
"He was a Guardian of the Whills, once. He made a vow, and he has already swore to me that he will keep it, to the death," Luke said.
After that, they were off. Master Luke had ordered Artoo to stay with Han, then moved off to another compartment, to speak to the girl. Then, they arrived at Jakku and he left the ship. With him was that small girl, who strongly resembled young Mistress Padme. That was curious. Why had he thought of Mistress Padme, after so many years? He didn't know. After a while, Luke returned and the ship took off as soon as the door closed.
Artoo wheeled himself over to Master Luke, beeping an inquiry. Luke had been bent over, his head in his hands, but when he heard Artoo, a smile formed. "Yes, I want you to remember this. In time, you will need to carry a message." Then he pulled a data chip out of his pouch. Artoo knew to accept it, and Master Luke dropped it in. "When you pick up these readings, the time will have come." Then he stroked Artoo's dome. "Now, I need to rest. Please leave me."
Artoo did that, a mournful whistle bidding him goodbye.
Jakku. He knew that. Could it be, after all this time? Had the Beebee unit been sent there to return with her (whoever her was. Artoo's memory banks seemed to be missing that important piece of information)? It was a couple of days, but the Beebee unit did arrive on D'Qar. However, Artoo did not detect the readings he was looking for. The little droid did come over once more, introducing himself as BB-8, once more trying to begin a conversation. Threepio reminded him that Artoo was on low power, and again expressed his fear that it was permanent. After that, they left together.
He went to sleep again. Maybe it would be for the last time...
Something woke Artoo. He verified the time on his internal clock. Several days had past since Threepio and Beebee stopped by him. But now, Artoo was picking up the blip that had been scanned by his sensors, that he had been searching for, for so long. He ran three dozen more scans, verifying his readings.
Finally, as if in confirmation, BB-8 rolled over, whistles and tweets sounding out of him excitedly. Artoo queried further, until a familiar voice was heard.
"Artoo-Detoo, you've come back!" Threepio said as he approached. Artoo beeped at him and he asked, "You've found what?" When Artoo answered him, he sounded reproachful. "How dare you call me that!" After Threepio smacked him, he asked again "Find Master Luke now? Come Artoo, we must go tell the others at once!"
The three droid entered the war room, and found Mistress Leia there. She was turned away from them, but Artoo's readings on her body language told him she was sad.
Threepio translated. "General, excuse me, General. Artoo-Detoo might contain some much needed good news."
Mistress Leia sounded anxious. "Tell me," she implored him.
Moments later, Artoo rolled himself into position and accessed the file he had kept safe all these years. A star chart beamed to life. Beebee-Eight whistled eagerly, went to a pilot, collected a data chip and, from in front of Artoo, added a missing section to his image.
It showed a path passing through many systems, but ending in one place. Artoo knew what would be found there.
"Luke!" Mistress Leia called out, sounding breathless. Excitement roiled the crowd, and plans were being mapped out. But Artoo wasn't paying attention to them. He saw the girl. She had grown, was taller now, but he knew it was her.
The crowd died down and he saw Mistress Leia walk off alone. He followed her, beeping to her. She turned, looked at him, as he went on. Then, she smiled. "Yes, I know who she is. I've known for a few days."
Artoo asked her how she knew. "She has it, she connected to it."
Artoo turned his dome around, examining her. He saw a lightsaber, hanging from her belt. He recognized it immediately, rocking back and forth, excited and terrified at the same time.
Mistress Leia brought his attention back to her. "You will go, with her and Chewbacca. Follow the map, find Luke," Leia said. Artoo asked her something and she chuckled. "I want nothing more than to go after Luke myself. But it's too dangerous, I have to stay here." Then, she crouched down, allowing his photoreceptor to look her directly in the eye. "Bring him home, Artoo." Mistress Leia looked up again at the girl, her voice growing wistful. "Bring them both home."
Artoo tweeted a vow to her that he would. After all, he had a mission to complete. And he always completed his missions, especially for the Skywalker family.