I never got to play Pokemon on handhelds as a kid, so my only experience is through emulators and romhacks as someone much older, so there’s no way to transfer Pokemon between games (that I know of).
So I just started naming mine by species, and treating it as if I just met a Pokemon I’d had before again in the wild. Different natures or IVs didn’t matter; aren’t YOU different over the course of your life?
Like “hey look, it’s Crockjock again!” if I wanted to do a run with Totodile. Same Pokemon, different adventure.