I have a theory that as the successor to the Kitetsu lineage of blades, Zoro wouldn’t actually need to upgrade his kitetsu at all but instead power up his current Kitetsu to surpass the first by making it black.
I believe that Zoro will first turn Enma black, then Third Kitetsu against Nasujuro and finally Wado Ichimonji against Mihawk in their final fight for the WSS
I believe that Zoro will first turn Enma black, then Third Kitetsu against Nasujuro and finally Wado Ichimonji against Mihawk in their final fight for the WSS