@EmeraldSky I'm not sure if this fits the prompt, because it's not that different from the actual Pokemon games.

When I was about 10 years old, I asked myself : "What if the player of Pokemon Ruby/Sapphire/Emerald came from a garbage truck instead of a moving truck?". I thought about that, but I didn't write it down at that time, so I'm going to write it down now :

Spoiler:
You start your adventure coming out of a garbage truck. Your mother comes closer to you : she is happy to see you, but she tells you that you smell terrible and that you should take a bath. Then, she shows you three dirty Pokemon who should take a bath as well. She asks you to choose which Pokemon will take a bath together with you :

-Treecko, the Grass-type Pokemon, has a type advantage against two gyms, the legendary mascot of Pokemon Ruby and the legendary mascot of Pokemon Sapphire. However, Treecko is weak against two other gyms.
-Torchic, the Fire-type Pokemon who gains the Fighting type after evolving, has a type advantage against two gyms after evolving. However, Torchic's evolved forms are weak against the last three gyms, the legendary mascot of Pokemon Ruby and the legendary mascot of Pokemon Sapphire.
-Mudkip, the Water-type Pokemon who gains the Ground type after evolving, has a type advantage against three gyms and the legendary mascot of Pokemon Ruby after evolving. Mudkip's evolved forms only have one weakness, but it is a double weakness.

Choose your starter Pokemon and take a bath with your new friend.
After you finish bathing, your mother tells your brother/sister to take a bath with a Pokemon as well. At first, you feel guilty because you were able to choose a Pokemon before him/her, but he/she tells you that he/she didn't want the Pokemon you chose anyway. Then, he/she picks the Pokemon who has a type advantage against yours. The Pokemon who is weak against yours stays with your mother.
After your brother/sister finishes bathing with his/her Pokemon, he/she challenges you to a Pokemon battle. Your Pokemon and his/her Pokemon are both level 5 and they don't know any moves of their own type yet, so this battle should not be too difficult.