Among Kang's disciples was a man who simultaneously served as an officer in the Song army. After the apprentice fell at the Siege of the Diaoyu Fortress in 1259, Kang adopted his daughter Zhang Zhi into the Assassin Brotherhood despite his fears that her drive may be fueled by a lust for revenge. Accordingly, he pressed on her to always prioritize duty over vengeance, but later that year, she defied his orders and infiltrated the camp of Möngke Khan. Though she was successfully assassinated the Great Khan, she was critically injured during her escape back to the fortress.
Recognizing that Zhi was forever crippled, Kang used this as a pretext to declare that she could never hope to be inducted into the Assassin Brotherhood. The true reason, though, was that he felt that her defiance in the name of vengeance disqualified her on ethical grounds. With that, he abandoned her to whatever her life was to take her next.
Personality and traits
Unlike other Assassins in history, notably those of the Italian Brotherhood who trained the legendary Ezio Auditore da Firenze, Kang subscribed far more strictly to the ideal that vengeance is unbecoming of an Assassin. Whereas Ezio's teachers tolerated his vindicative quest and, in Ezio's own words, guided him to learn to mature past it over time, Kang saw vengeance as the unforgivable, bottom line. In his philosophy, vengeance was an irrevocable dereliction of one's duty as an Assassin, the ultimate proof that an individual lacked the moral discipline to be worthy of the name.
As a result, he was suspicious of his apprentice Zhang Zhi from the start, from the sheer understanding that her passion for learning would be driven by the death of her father. When she assassinated the khagan against his own commands, in this eyes, this critical victory was not enough to justify her disobedience. The intention and motive behind her deed weighed just as heavily to him, if not more, than the consequence, even if that consequence was the death of a dangerous enemy whose leadership threatened all of China. Being an Assassin to him meant cultivating strict, moral discipline, and Zhi's actions, though beneficial, proved to him that she was not ethically qualified to continue serving the Brotherhood.
Consequently, Kang stands in contrast to not just Ezio's teachers of the Italian Brotherhood but the later Neo-Confucian Mentor Wang Yangming as well. While they disapproved of vengeance as antithetical to an Assassin's character, they had the patience to see their apprentices learn to grow past the mentality through firsthand experience.