This was just a headcanon of mine that escalated to the point of pain. So hurt with me.
C3p0 couldn't believe what he was hearing, R2 really had lost him mind there was just no denying it this time. The poor droid, he'll miss his antics. He was such a good friend, an ecentric one that has nearly fried his brains many many times. But a friend nonetheless.
R2 beeped in annoyance, a beep roughly translated to "Listen to me you Golden Shit." The droid did a little dance on his wheels before a compartment opened. Within it was a small disk titled "C3p0 memory".
"What is this? Have you had this all along, R2?" C3p0 asked his friend as he took hold of the disk. R2 beeped. "You stole it?! R2-D2 that is the upmost irresponsible behavior-" R2 beeped again. "Don't call me that!"
"Is everything alright in here?" Finn asked as he poked his head into the room. He was on his way to meet up with Poe, but stopped once he heard C3p0's yelling.
"Ah, Master Finn," C3p0 exclaimed in relief. "R2 was just telling me that he has a piece of my memory- from before the war!"
"Whoa, really?" Finn came inside the room, his eyes alight with interest. "That's so cool, have you plugged it in yet?"
"I- no.. my port is in the back. I can't reach it," C3p0 said sounding embarrassed. "Could you?"
Finn shook his head. "I'm afraid to, I don't have much experience handling droids. Maybe Poe can?"
"Master Poe, of course!" C3p0 did an upper body nod before setting off to find the pilot. He stopped suddenly and turned to the following human and droid. "What if I'm not supposed to have these. They removed them for a reason, did they not?"
R2 beeped as Finn placed a hand on C3p0's shoulder. "You should always have a piece of yourself," Finn said. "Even if it's painful."
[slideshow transition]
"Of course I can do it," Poe said as he flashed his Winning Smile (it should be trademarked at this point really). He took the disk and walked behind C3p0. "This might feel weird, I'm assuming." He plugged in the disk.
He was right, it did feel weird. But then it felt worn down and saddened, causing C3p0 to gasp as his memories came rushing to him. "Oh! I did have a master before Alderaan!" He exclaimed. "Master Anakin Skywalker! Oh he was such a good, kind lad. He- he left me to become a Jedi. I was in charge of taking care of his mother.. but she died and he came back! He took me with him! I- he... he went to Mustafar... he killed so many..." C3p0 felt horror and pain course through him, and he was sure that if he had a heart- it would break. "Master Anakin became Darth Vader..."
"I'm sorry," Poe whispered to the distraught droid. By now, everyone had known the tale of Anankin's descent to the Darkside. C3p0 himself knew, but he didn't know the importance of the man.
C3p0 shook as he collected himself. "It's perfectly alright," he said as he turned to face the three. R2 beeped. "No I am not lying! I'm perfectly alright now." But he wasn't, not really. Apart of him would always wonder if Anakin ever remembered him during his days as Darth Vader, and if he did- did he ever miss him? Now that he could remember, he remembered his days on Tatooine. He remembered missing Anakin as he tended to his mother and her new family. Anakin was respectful of droids, even treated them like people at times. R2 beeped again as he bumped against his friend. "Oh! Stop that, R2. Behave yourself. I still don't understand how you stole my memories, or how you got away with it for so long."
R2 beeped in the way he always beeped when he did something bad. "You took it before they could destroy it?" C3p0 repeated. "Oh, I should have known." He did an upper body shake. "But, I do appreciate it my friend," he added sincerely.
He would cherish him memories, the good and the bad, for the rest of his life.