Maybe it just hard to make a story about it.
Oh c'mon how hard can it be.
All the pirates who are after the One Piece...head for the New World, the second half of the Grand Line. However no one has ever fully explored it except for Gold Roger, King of the Pirates. The New World has ruined many pirates' dreams and ambitions.
Now, D. Lucy, a boy whose has eaten the Moment'-Momen' Fruit, will venture into the sea, to become the King of the Pirates.
The guys names actually Lucy with an artstyle very familiar with original One Piece. Take random girls for normal stuff and reserve Nami/Robin for later updates where you CANNOT dominate them but can have sex. They're important NPC which gives quest items. Having the name Lucy can circumvent how this new guy so easily gets laid in Dresserosa.
You start your journey with a navigatable small boat (Like Pokemon water areas), You meet a random-girl in the water about to die. You save her but you're naive. She gives you blowjob as she explains how things work in these parts of the Real Pirates. She steal your money and everything (she is NOT nami) and turns out was working for Baroquee Works (Crocodile syndicate). You go to the island to get your things back where you learn only 8 days ago Zoro from infamous Straw hate pirates destroyed the whole company and thats why she was tasked to steal from you as to gain their assets back. You can write a bunch f stuff here with little things to do as you learn you're nothing compared to Luffy and the pirate world is too harsh. You decide to charm the new acting leader of the baroquee works (obviously a sexy office piratey woman) while the company tries to figure out why Crocodile isn't replying. Later you can get to know the only way to get to next island are the eternal posts which is with Ms Valentine. Also can introduce Miss AllSunday (Nico Robin), She can advance the quest while giving you some tasks to fullfill (basically using you) adn in reward will give you a handjob (with no real hands) when you exceeded hers expectations by finding out an alternative way to SkyIsland, where she might have sex with you. While now Robin is gone with Straw hat Pirates you can explore Skypeia and maybe 1 girl there added to your crew.
Ok i am bored but I can write the crap out of it. You can maybe set everything into just one island with 10 characters if you get the pacing nice enough. It's not that hard to have original canon intact while still having some "gifts" from Robin, Nami (You trick her into having sex while she was seducing you for some secret, She will have her revenge though because she's Straw Hat Pirate blah blah)), Baby 5, Camie, endless potential and really REALLY easy to write stuff about. that's just 5 minutes of rant.
C'mon people. Please make a good One Piece game.