Izuku Midoriya
Izuku Midoriya is our main protagonist who has changed a lot since his original prototype. His hair is a big element of that, going from being down and being called Hot Topic Deku by fans, to having super spikey hair. His costume has also changed significantly from the first concepts, going from a bunny mask with sharp teeth, to a mask with a cloth mask. Then finally, he modified his costume to aid his quirk and rarely wears his mask anymore.
Ochaco Uraraka
Ochaco Uraraka is another main character in this anime, and her original concept art had her as a completely different character with a different quirk. She originally was supposed to have a quirk that would turn her into a giant, and that quirk was given to a different pro hero, with Ochaco getting a zero gravity quirk instead. The manga and the anime do not change her design much, keeping her appearance and costume pretty much the same.
Toru Hagakure
Toru Hagakure is another student at UA, who originally was supposed to be a male character. She has an invisible body, but her original design had shown her with more accessories, which would have made her more visible. The manga and anime have her wearing either just her school uniform or a pair of gloves and shoes, which doesn’t leave much to change.