couple of things that i honestly think will help ur fanfic out. Lose the harem idea no offense but ur romance writing sucks the r18 scenes are so bad it physically hurts me. His bounty alias needs to change whats up with the naming sense its honestly cringe something simply like "white tiger" thirteen not only fits the theme of one piece better it just fits the character more. Again with the naming of his moves less is more why does everything have god in it shadow god ,slaughter god, star god just keep it simply his movement skill could just be star step and that thing with merry something simple like star sign would do. The idea of nightmare as a whole is super awkward u already had smoker describe it as him being feral and just left it as a instinct thing he needs to control, the split personality thing just dsnt work. Your fic isnt bad honestly the characters cool and i feel like ur eager to get on with ur own arc soon i feel like just him meeting and figuring out the mink world in one piece would be a super interesting fanfic on its own its just these small things that arnt adding anything to the story that break it up and make it awkward and cringy to read. I hope if u read this u dnt think im just bashing you i wouldnt have read up to here if i thought this had no worth keep going with ur writting maybe you will think about my criticisms as just that and try to if not change atleast improve on ur style.