Erins character was based off of young Joseph Joestar, silly and charismatic in both younger and older years. This was later changed to Erin being a bit more aggressive and vocal as he was young, and more smug and charismatic (but also calmer) in part 4. Lots of changes are being made to this character, especially his actual name since “Erin” is just a nickname. Picture of this design, dubbed lovingly “Erin, v1.5” https://ibb.co/QdCq8QB