Significance of first one's grades?

Still not sure if they are grades or what but I’ve noticed that the ones I use more often are higher letters and are getting higher. Can anyone tell me why any of this is important?

I do believe they get stronger. But i’m sure someone has a better reply than this. But i have noticed it seems like they scale upwards, more health hit harder. that sort of thing.

yes, the more you use them, the higher their grade is. i think you need to use a first one twice to get it from B to B+ or S- to S. It’s like 1/3 of a grade every 2 battles

Thanks for the good replys guys! This confirms my thoughts aswell

Altough the first 3 or 4 first ones u get while defeating them are still very weak