"Ah, bonjour!" Riko said, doing a little bow and a wave. "My name is Riko Ketchum, it's nice to see you!"
"Oh, hi!" Roy smiled. "So, I guess you're from Kalos?"
"Oh, no, Kanto actually!" Riko shook her head. "My dad's from there, and that's where I grew up."
Roy nodded. "So, uh… your mom's from Kalos then?"
"That's complicated," Riko answered. "Ehehe… there was something about a massive argument, so technically speaking I have one mom but that's just the average."
Roy looked blank.
"I mentioned the argument, right?" Riko checked. "Well, there was an argument. So I'm, uh… eesh, I keep forgetting the term Uncle Giratina used… I think it's, a quantum superposition! That's the word. So I'm about a twelfth Kalosian because my mom is one sixth from there, there's one from Kanto, Hoenn, Sinnoh… I'm about eight percent Latias… believe it or not I've been told this is the less complicated option."
Roy was agape. "How is that the less complicated option?"
"Yeah, you'll see," Riko replied, shrugging.
AN:
If there's rumours going around that she's Ash's kid, this seems like the most reasonable compromise.