Wait when we get to his clash with Nusjuro/Mihawk where Kitetsu, Black Blade and Ryuma-Shimotsku lore will be fully explained. There's 2 foreshadowing IMO;
1) His father Arashi had a duel with Mihawk and lost. Note the death of his description stated he was killed by a "pirate". Above all, Mihawk pulled the common trauma trope reaction when Zoro pulled the 3 sword style which led me to believe that was Arashi's move and that was the main drive for Zoro which is why Mihawk has faith in him (revenge is a strong motivator). How else would a complete rookie from the East Blue know him when no one who has never been to the Grand Line know who he is?
2) There is a clear parallel between Zoro's sensei Koshiro and Nusjuro (same glasses, eyes, nose, neck width and Wano attire). Ryuma who looks virtually similiar to Zoro was Nusjuro's sensei or Wano Shogun of his time etc..
Nusjuro who is the holder of Shoda Kitetsu which means "First Demon/Ogre/Oni Piercer". I believe he succumbed to the Kitetsu curse and went berserk against the people of Wano so Ryuma fought and defeated him, thus becoming a sword god.
Either way, 100% we're getting the Kitetsu-Nusjuro-Ryuma flashback when Zoro meets him.