>>50030070Here's my take on it.
Red's defining personality trait is his determination to be the best, pushing him to ever greater heights, which aligns perfectly with Charizard's dex entries that talk about it searching out strong opponents to hone its skills. Plus Charmander is at a huge disadvantage in Kanto, just like how Red starts out as an underdog, lagging behind Blue.
Blue is known for his arrogance and direct, brute force battling style. Blastoise is similarly arrogant, tilting its head up and sneering in all its official art. And again, it's progression reflects Blue's. Squirtle is laid back and confident, and has no trouble in early Kanto, letting Blue breeze through the early gyms like he canonically does. But as Squirtle evolves, it gets more fearsome and aggressive until it literally sprouts cannons, paralleling Blue's battling style becoming more ferocious as he gets more nervous about Red beating the odds and nipping at his heels.
And Green is the trickiest of the three, letting the boys squabble over the champion title while she goes off and does her own thing, just like how Venusaur forgoes the direct offense of the other two in favour of relying more on status conditions and recovery in battle.
Honestly you can make a case for any of the characters with any of the starters, but I think this is the one that lines up best
