This is a joke. A little jk fan theory I cooked up. I hope you enjoy but don't take it seriously.
Jason thought he knew his best friend pretty well. They'd fought Gaea side by side, they'd been through a lot together. So when Leo said he had something to tell Jason and Piper he didn't expect to be surprised. He walked hand and hand with his girlfriend, talking and laughing with her.
They'd promised to meet Leo by bunker nine, where the son of Hephaestus was calmly waiting.
"Hey Leo, what's up?" Piper asked, smiling.
"I have something to tell you bu you have to promise not to freak out." Piper frowned and Jason frowned also.
"Leo-" he started.
"Promise." They begrudgingly promised.
"I'm not a child of Hephaestus. I'm not even the real Leo Valdez. I'm a tinker fairy, born when the real Leo laughed for the first time as a child. The real Leo Valdez died with his mother in the fire, bu because Leo had such a big role to play the gods made me into his mirror image, gave me fake memories for reference, and Hephaestus, devastated by the loss of his son bestowed on me a gift." His fingers lit up with a small flame. Piper stared and him and shook her head.
"What are you trying to pull Leo?"
"Nothing I'm completely serious!"
"Leo did you hit your head? You're not a fairy." Jason told him, worried about his friend's sanity.
"I didn't hit my head. You want proof? I fulfilled my job by helping defeat Gaea. I can turn back into a fairy any time I wish." And with that "Leo" shrank into fairy form. Mostly he looked the same, except he had wings, was tiny, and no longer wore a toolbelt.
"L-Leo."
"That's not actually my real name. Look, you guys are amazing friends, but I miss Pixie Hollow. I might visit you no and then, but its unlikely. Goodbye."
I really hope you enjoyed this, feel free to write similar stories with other characters or even Leo or continue this one or whatever, I'm probably not going to write another cross over like this one.