Board Thread:Consensus Track/@comment-28908658-20190217001843/@comment-1512913-20190217105247

Are you serious? You are pushing your propaganda a little bit too far now. As already explained to you, it refers to biological gender, sex, the only relevant one for us and the only one given in the databooks.

The reasosn why the Tailed Beasts are referred to as it, are because:
 * they weren't conceived through the act of sexual reproduction, but magic
 * their genitalia haven't been shown

For Black Zetsu, it's animated will, hence can't have biological gender. Katsuyu is a slug and slugs are hermaphrodites, so both male and female.