This is an idea for now. I don't know when I will start the project. I was thinking of a Pokemon FireRed ROM hack while listening to the Pokemon XD: Gale of Darkness OST (I'm not using the songs from that game though). Hope you enjoy it! Any feedback and extra ideas are welcome!
Story: In the Italia region, a strange type of evil is ravaging the world. Giorno Giovanna, a young teen with the Stand named Gold Experience, has noticed how many rogue Stand users have appeared within this new region. With the help of La Passione's Bruno Bucciarati, Narancia Ghirga, Guido Mista, Pannacotta Fugo and Leone Abbacchio, the fight to save the region from the rogue team La Squadra di Esecuzioni, and their boss, Diavolo is a mandatory mission. Victory won't come easy, yet it's possible.
Town/City/Village names: Nuova Casa Town, Grande Oro City, Lago Crestato Town, Terra Irrigata Town, Aranceto Village, Leggenda Dell'acqua Village, Giovane Stella Village, Bellezza City, Il Coraggio Village
Gym Leaders: Bruno Bucciarati (Specialty: Water and Psychic, located in Grande Oro City), Leone Abbacchio (Specialty: Dark, located in Leggenda Dell'acqua Village), Narancia Ghirga (Specialty: Fire, located in Aranceto Village), Guido Mista (Specialty: Steel, located in Bellezza City), Pannacotta Fugo (Specialty: Poison, located in Terra Irrigata Town)
Enemy Trainers/Stand Users: Cioccolata, Secco, Sorbet and Gelato, Diavolo (main story boss), Carne, Doppio (only challenged in Squadra Downfall story after defeating Diavolo in the main story)
Enemy Teams: La Squadra di Esecuzioni (Risotto, Melone, Ghiaccio, Formaggio, Illuso, Prosciutto, Pesci)
Battle Formats: Single, Double, Rotation, Squad (Squad vs Squad, e.x. La Passione vs. La Squadra, accessible after completing main storyline), Stand (Stands only), Requiem (requires Requiem Arrow)
Obtainable Items: Requiem Arrow (obtained after defeating Diavolo, enables Gold Experience to mega evolve into Gold Experience Requiem), Stand Arrow (obtained after full completion of the StandDex and National Dex, enables wild Stand battles and higher shiny chances, replaces Shiny Charm)
Regular Trainers/Stand Users (can ask for a rematch at any time): Jotaro Kujo, Koichi Hirose, Polpo, Jean Pierre Polnareff