Zero is an assassin employed by the Adjudicator, and the leader and mentor of his own group of assassins. He is the secondary antagonist and a major opponent in John Wick: Chapter 3 – Parabellum, during which he fights against protagonist John Wick on several occasions.
Zero is a trainer of a group of ninja-assassins. When not teaching, he works as a street-food sushi-chef. He is a fan of John Wick.
Events of John Wick: Chapter 3
Zero is hired by the Adjudicator on behalf of the High Table to kill John Wick. After John returns from his meeting with the Elder, Zero and his students confront John Wick and trie to kill him, but John fights them off and flees to the Continental. Zero pursues him there but before he could kill him he is stopped by Charon, who informs him that no business is to take place on Continental grounds.
John then goes inside to meet with Winston and seat down on a couch while waiting for Charon to go and get him. Zero attempts to sit down next to John but John moves to a chair to get away from him. Zero then tells John Wick that he is a big fan of his "work" and that they are both the same as "masters of death", but John rebukes the latter part.
Later, after Winston refuses to step down as manager of the Continental and John Wick agrees to defend him, Zero is instructed by the Adjudicator to kill both of them and given an army of highly-trained mercenaries to assist in the task. However, John manages to fight through Zero's men and two of his top students, the Shinobi, before facing off with Zero himself. After an intense duel between the two, John defeats Zero by ramming him through the chest with a katana. As the two lay exhausted, Zero compliments John on his skills and states it was an honor to fight him, to which John agrees that it was a good fight. As John gets up and walks away Zero attempts to do so too only to instead slump over and die.
Despite his job as an enforcer, Zero does not seem to let it affect his personal life. He seems to take extraordinary enjoyment from fighting, and both he and some of his students are big fans of John Wick to the point that they let him recover between fights instead of hitting him when he's open; during their fight in The Continental, he quickly admitted to Wick that he's a huge fan of the latter's work and abilities.