Of course, the nature of Kuina's death is ultimately unimportant in light of the motivation it provides Zoro. When Luffy (Iñaki Godoy) first meets him in Episode 1, Zoro makes it clear that his ultimate goal in life is to become the greatest swordsman in the world. It's the fact that he vowed to be one of two people to accomplish this ambitious task only to lose that other person, viewers find out in Episode 4's flashback sequence, that drives him to do so.
Perhaps complicating matters is a conspiracy among some "One Piece" fans that Kuina is still alive. One detailed theory full of late manga spoilers circulated by Reddit user dodomangus proposes that the Marine swordsman Tashigi is actually Kuina. Zoro remarks that Tashigi resembles his childhood friend as soon as he meets her, but the manga has yet to ascribe any significance to this resemblance.
If this theory is true, then the Netflix "One Piece" series may have omitted Kuina's cause of death to make room for the reveal of her survival. Since this is currently within the realm of conspiracy, however, viewers can assume for the time being that the live-action version of Kuina also died after falling down a flight of stairs.
