Reminds me of Little Gigant from Inazuma Eleven final arc. Based on a fictional African country, the team is a full expy of the main Japan team, and trained by MC's Grandpa. MC's love interest also temporarily assisted them before returning to Japan team.

Shame Orion retcon them to non-existent. They literally wore training weights throughout their tournament until the final match. I quite like how the goalkeeper is originally the main striker, while his substitute also can adapt fast.
https://youtu.be/APglbtci9Mo?si=XccXRz3d7xxMej03