To cut to the chase – Zoro has already been taught Oden Two-Sword Style, he learned it from Shimotsuki Koushirou (his master from Shimotsuki Village).
From the latest chapter we learned that, in the words of one of the great Chads of One Piece, that Oden Two-Sword style is the greatest sword style there is.
We also saw his Two-Sword Style having been learned by 4 of his Scabbards, so it’s something that can be learned and is not unique to him only.
We know that Zoro’s sensei, and Kuina’s father, Koushirou is the son of Shimotsuki Kozaburo – a master swordsman and swordsmith who left Wano and ended up in the East Blue. He also crafted two swords Zoro has – Enma (originally Oden’s) and Wado Ichimonji (originally Kuina’s).
I think Oden’s Two-Sword Style was influenced (if not outright taught) by Kozaburo and that this style, being the greatest, was passed down to Koushiro and then to Zoro. Zoro originally fought with two swords, and he was taught Oden’s Two-Sword Style – and then when Zoro upgraded to three-swords, he build his three-sword style around the foundations of what he had been taught which was Oden’s two-sword style.
I’m sure that Oden crafted what Kozaburo taught him and made his own – as I’m sure Koushirou and Zoro updated/adapted based off their styles too. But I think the foundation of their styles are one-and-the-same. Further proof for this theory? Look at the comparison:
They are nearly mirror images of each other – because Zoro is left-handed.
