1. Boa Hancock as a child until she becomes a Shichibukai. Her time as a Kuja Pirate, then slave, escaped and helped by Rayleigh to her rise as Queen of Amazon Lily. She's a pretty difficult character personality wise, but I think if it's her journey, where we see her story and inner monologues, she'd be a lot better. Make the epilogue her in Mary Geose again in Pangea Castle as a stark contrast to her times as a slave.
2. Eustass Kidd. His backstory has a lot of potential. Growing up in an unaffiliated island ruled over by a gang and additionally having multiple other gangs — Killer, Heat & Wire — to rival against is already a great start. His childhood crush dying and Kidd uniting the different gangs under him to defeat the island leaders? That'd be lowkey amazing to see play out. Could even go further into Kidd's journey into the Grandline and maybe what he did in the timeskip. Good place to end it would be his defeat at the hands of the Redhair Pirates.
3. Dracule Mihawk. Similar to Boa, I think he's best around other characters rather than a standalone character. But with the inner monologue and purpose, he'd be fun. His early days rivalling Shanks and how he became the World's Strongest Swordsman would be the ideal stories to tell. IMO it'd be a lot less plot heavy due to how isolated of a character Mihawk is—which could be explored, discovering why he initially didn't enjoy company—but would satisfy people who want big, dramatic fights.
In general I think any of those 3 would help make the One Piece world feel more lived in and give us good contrasts to the Straw Hat's adventures.
Crocodile deserves one. An antihero story following Crocodiles journey. There are two main stories I’d like.
1. Crocodiles origins - His original crew -> Him fighting through the Grand Line -> Fighting Douglas Bullet -> Fighting Primebeard -> Giving up and Discovering Pluton -> Creating Baroque Works.
2. Crocodiles time post Baroque Works. Starting with Impel Down written through his Point of View -> Marineford -> Amassing his strength wealth and underworld connections -> Creating Cross Guild.
Didn't even think of this. Crocodile novel would be next level. His early years before he settled down in Alabasta were compared to Luffy's by Oda IIRC. Would be a great way to characterize him too.
