Got a plan at the minute for the Solgaleo thing.
So when you go after the Alola Lengends, the first part will involve taking care of Nebby to get her to evolve into one of them, which one will be random but it will be explained that the other one is always male (so not always Solga, could be Luna too)
The MC will then travel to an alternate universe with Nebby to find a female of the one he couldn't get in his own universe