And how exactly can Ushimaru be Zoro's father, when Zoro was born in East Blue, and he goes by the Surname Roronoa.
And before you say "He took his mothers name", why would he do that? Ace had two reasons to not take his fathers name.
Why would Zoro not take a proudful Samurai name like Shimotsuki?
And then again, how did he make it to East Blue? Ushimaru sent his mother East Blue after she got pregnant? So where did the mother with the last name "Roronoa" come from, cause that damn sure isn't a Japanese/Wano surname.
She's an outsider, who made her way into the Country?
Now, we are just getting super convoluted here.
Ushimaru, married a women from outside of Wano, with the last name of Roronoa. To "Protect his wife and child" he sent them on a boat, where they sailed across the entire World, through dangerous Ocean and they somehow made their way to Shimotsuki Village all the way in East Blue. Zoro for some reason, despises his father, and decides to take his Mothers Surname, but still ends up training under a member of the Shimotsuki Clan.
That about the gist of it?