Gen 2, start in Ecruteak city
>adventure starts with you and a friend sneaking into burned tower
>Morty is sent by your parents to find you, you've both been missing all day
>he catches up and scolds you, floor gives in, the 3 of you see the beasts wake up and run off
>friend gets super excited, immediately wants to run off after them
>Morty drags your asses back to town, your parents and other worried townsfolk are outside
>after Morty explains what happened Eusine has an outburst because suicune obsession, decides it's destiny and you two were chosen so he wants you guys to go on a journey
>convince your parents it'd be good for you/teach you some responsibility
>next day Elm shows up to give you your starters, friend's parents didn't like the idea of them going out on a journey so friend doesn't get one
>Morty tells you to come back and challenge him once you've grown a little stronger(team of 2 at level 10 minimum)
>friend becomes jealous when you leave, he steals the starter with type advantage against yours, runs off
>catch some mons and train a bit, maybe side quests or hit another gym
>come back to fight Morty, find your friend, wants to beat you to prove his parents wrong, becomes dick rival out of obsession
>proceed in whatever order you like Ecruteak is fairly central so there's only a few places you can't go early on and we all know dynamic level scaling is best/easiest fix for breaking linear progression
>rival joins team rocket, gets very misguided throughout the adventure
>end of Johto it's justified that you catch the legendaries and always win because you're the trainer who grew with their pokemon instead of falling to jealousy and bitterness like your rival who never got past the elite 4, teach them a lesson and they apologize/get their life back together
>get a 2nd adventure through Kanto after you're champion and it's a more friendly but still competitive rivalry
>rival becomes final champion battle