While Rei Ayanami is a human-angel hybrid created by Gendo and NERV, Kaworu Nagisa is an angel-human hybrid created by SEELE. Unlike Rei, he is more Angel than Human and describes himself as being unable to resist the call of Angels to possess Adam. While Rei is created using Yui Ikari, the other half of Nagisa's DNA remains a mystery. He hates SEELE and would destroy them if possible for creating his cursed existence.
Differences between Canon and WarhammerEdit
Kaworu Nagisa is the subject of the second difference between Canon and the improvement. While Shinji discovers the core Warhammer rulebooks containing the four main races of Space Marine, Chaos, Ork, and Eldar, Nagisa discovers the Tau and their concept of Greater Good. He becomes willing to commit lesser evils in order to serve the Greater Good and becomes convinced in his own way that it is best for significant parts of humanity to be destroyed in order to form the rest into a perfect hybrid collective, destroying the individual will and ambition in order to forever abolish war, hatred, and inequality. While in Canon, Nagisa appears only in the last episode as a psychopath who ultimately demands that Shinji murder him, in the improvement he appears much earlier, is active and attaches importance to his own existence, and is perhaps the greatest threat. Though his goal is arguably worthy of being called the Greater Good and a much lesser evil than the Third Impact goal of Gendo and SEELE, Shinji and NERV nonetheless opposes it on the grounds of preserving free will and allowing humanity to decide their own destiny.
Kaworu has a romantic relationship with Asuka which leads her to throw away her pride and become a significantly more balanced and capable pilot and team leader. While part of the relationship was manipulation, Kaworu states that he does indeed have feelings for Asuka. He later gives her a pendent which he states as symbolic of the Greater Good, passing it on to her as the worthy successor even though he continues pursuing the Greater Good in his own way. His only later appearance to Asuka is a blatant manipulation leading to Asuka forcing Shinji to give an oath that he would allow Asuka the privilege of killing Kaworu.
Shinji describes Kaworu as being so polite that you forget he is about to stab you in the back. Kaworu does have a practice of chronic backstabbing and of killing anyone who gets in his way or possibly could.
As an angel-human hybrid, Kaworu has significant power on his own. He is shown as having the power to destroy a small military facility on his own in a matter of minutes and singlehandedly destroys a significant force of psyker Grey Knights with power he gathered from killing psykers across the world. Unlike in Canon, he never gains an eva of his own, instead gaining a customized Trident Warborn with two incarnations. Its first is a ranged specialist capable of destroying an angel in a single shot. Its second is significantly different, a melee specialist which can teleport and move at blinding speeds. He seems to have access to both an AT Field and its polar opposite, psychic power, including some limited prescience. Despite his abilities, Kaworu Nagisa remains hesitant to tangle directly with Shinji Ikari because their battle would be too evenly matched and Kaworu could not foresee the conclusion.