As a multishipper, I actually have two different pokeani AUs, and both of them are equally canon to me (actually, it's more like one AU and two different routes).
In this AU, Ash and Misty realize they like each other when they're almost 20. However, after some misunderstandings and a lot of miscommunication (or the lack thereof), Misty gives up and she's too proud to confess her feelings. So she decides to go to Kalos, since it's always been her dream and she needs a change of scene.
She meets Serena in Lumiose City (I even started to write a fic about that) and they develop this one-of-a-kind connection, which is new for both of them. The first time Misty fell in love, it was slow. Literal years had to pass before she could admit to herself that she had a crush on Ash. But now? Now she is perfectly aware of how down bad she is for Serena. This lovely girl she has just met, who is kind to every single living creature, who is like a princess.
Serena's case is the opposite. When she fell for Ash as a kid, it was basically love at first sight. It was intense since the beginning. Now she doesn't even know she likes Misty in that way. And, of course, she has no idea of how much Misty wants her. Sure, Serena needs to be sure she's always okay, she wants to buy all the desserts and clothes that Misty wants but it's because of her own personality and also because that's simply how normal friendships are. Sure, she thinks this friend in particular is especially beautiful and determined and smart. She's just so lucky to have her, you know?
That's how they end up spending the entire summer holidays together, travelling through Kalos, accidentally brushing their hands from time to time, staring at their lips for a bit too long, feeling their racing heartbeats every time they braid each other's hair... Your average girly things. However, Misty needs to go back to Kanto. And, once again, she's unable to confess her feelings, except this time she decides to write a note, at least. I'm keeping what happens next for my fic, but long story short Misty chooses not to leave and they start an absolutely wonderful relationship.
Here's where my own canon splits into two different routes. In one route, everything is perfect and they get married at 24 because that's how sapphics work. In the other route, they eventually become codependent and break up at 24, because that's also how sapphics work. In this second route, Ash grows a spine and tells Misty he's never stopped loving her so they get married in their late 20s. Serena's like "when you wake up next to him...🎶" for a while, until she moves on (and she starts dating our favorite Lumiose's gym leader who has transitioned and goes by Clem now). In both AUs, all of them are great friends and don't hold any grudges.
