This is a one-shot I came up with, though I might eventually write a second chapter. It is a possible, though unlikely, reveal for a story I might write in the future. The movie is slight au, but still ends basically the same.
I do not own RotG
The Guardians had just gotten back to the Pole after the battle with Pitch, and the ceremony to make Jack a Guardian. They entered the Pole and were walking through the workshop when Jack stopped. He then looked up through the skylight, where the Moon could be seen, shining through.
"Thank you Mitsuka!" Jack called. A soft, female voice responded with 'You're Welcome', although only Jack could hear it.
After Jack said that, the other Guardians glanced up at the Moon, and saw it briefly glow brighter. However, when they blinked the glow was gone.
"Uh, mate, what ya doing?" Bunny asked.
"Thanking MiM," Jack replied.
"But why did you call Manny Mitsuka?" North questioned.
"Cause that's her name," Jack answered.
"But Manny is boy," North said, confused about what Jack was saying.
In a turn of events that surprised and confused everyone but Jack, Jack bursted out in laughter. "You think... Manny is a... boy!? No wonder she is irritated with you guys a lot."
"Okay mate let's say that we believe you and Manny is a girl. How would you know that, let alone her first name? Even us who Guardians for a long time, and alive before Manny was even born, don't know her first name. We only know her as Manny or MiM, and sometimes Tsar Lunar. You're only three hundred, and I find that hard to believe." Bunny said.
"Well for one, I am much older than you all think. Second, how do I know her name? Easy, she is my older sister."
"What!?" All the Guardians yelled, Sandy using his sand. How could Jack Frost, mischievous trickster, be Manny's brother.
"Yep, though I don't live on the Moon. I mean, I used to, but I don't anymore. Haven't, at least not permanently, for 300 years." Jack explained. "Anyways, didn't you say something earlier about a party in celebration?" And with that, Jack walks away, heading to the kitchens.
"Hey, wait." The Guardians yelled after Jack, but he seemed to not hear. Well, they would just have to interrogate him later, they had a party to throw.
Well, that was shorter than I normally write. Hoped you enjoyed!
Note: Manny's name, Mitsuka, is a Japanese name meaning "the beauty of the moon", "the gracious moon", and "child of light",