It's oda keeping to a joke. He's a man who acts very girly. He didn't say he was transitioning, the bath scene was no meaning behind it. Just ha, they're keeping up with the joke to the point he's in the bath and no girl gives AF. The character sheets refer to to kiku as a male with the heart of a female. Oda didn't say in interviews this is what his character is supposed to represent, or some political BS. He's a MAN.