Listen fanfic blogs love talking about being monster fuckers and making monster aus of favorite characters, but... maybe I wanna be the monster. Maybe I want to be caught and fawned over by a weird human who's way too into it. So I'm gonna go over some characters I think would be monsterfuckers <3 honestly Robin is a strong contender. She's very calm and not much phases her, and she's been called a monster herself for her whole life. Plus her being so close with Franky and calling Jinbei handsome. I can see her getting a monster to open up to her despite being human, willing to play the long game to get you to trust her. Your form doesn't bother her, and you think her devil fruit is pretty cool(it's good for getting scratches in hard to reach spots.) Ace for similar reasons. He's a monster too- why would he give a shit what you look like? He's just so friendly you find yourself coming back, and you get pretty fond of his devil fruit if you're cold blooded.
Sanji I can see going for it too but he's so overbearing about it you might get scared away. Declarations of passion and going on about how you're beautiful, that he sees you for the sweet, wonderful, unique, gorgeous, etc. Creature that you truly are! Please, allow him to shower you with the adoration you truly deserve- Wait, where are you going? Probably only gets you to talk to him again with food. I can see Law being one too, but he doesn't deliberately seek it out. Meets you and has a little "what does this mean about me?" Moment. Also kind of a dork if you remind him of something from one of his comics... he'll never say it but he thinks you're so cool. Kidd would but it starts more like "fuck yes we're the scary bad guys, of COURSE I'm getting this thing on board to wreak havoc with us!" Aaaand develops into "of COURSE I'm fucking it! Hopefully!"
This is getting so long for an ask but Marco also. By extension the WB pirates in general, they're mostly human but I think they have one Fishman? You're sort of a novelty, but they've got a reputation for picking up strays and outcasts, nobody really cares what you look like at the end of the day. Marco is used to preening himself in his Phoenix form, and he'll help you with any grooming or shedding. You mumble something about being hard to keep fed, and Thatch just laughs. Did you forget how big Whitebeard is?