It was never specified whether Dororo is a girl or boy (in the anime) but it has been confirmed that Dororo’s sex is female. I use he/him pronouns for Dororo because that’s the way he is referred to in the show. I’m not gonna go out of my way to use she/her pronouns.
Dororo responds to he/him pronouns and seems comfortable with them so when referring to Dororo, I use he/him. Because that’s the way Dororo is referred to in the show,