Kaworu Nagisa (Japanese: 渚 カヲル, Hepburn: Nagisa Kaworu), real name Tabris (タブリス, Taburisu), is a fictional character from the Neon Genesis Evangelion franchise created by Gainax. In the original television series, he is the pilot of a giant mecha named Evangelion Unit 02 for the special agency Nerv, as well as the seventeenth and final member of the Angels which threaten humanity and that Nerv is meant to fight. When he arrives at Nerv, he meets Eva-01 pilot Shinji Ikari, showing great affection towards him. After revealing his nature as an Angel to Shinji, he asks him to kill him to allow humanity to survive.

The character, originally conceived by Gainax as a cat controlling a boy, was supposed to appear in the series' twenty-second episode. After several changes, director Hideaki Anno and screenwriter Akio Satsukawa decided on him being the last Angel, and he was included in the twenty-fourth episode, "The Beginning and the End, or 'Knockin' on Heaven's Door'". He later re-appears in subsequent works in the franchise, including the Rebuild of Evangelion films, video games, the original net animation Petit Eva: Evangelion@School, and the manga adaptation by Yoshiyuki Sadamoto. His role is notably significantly expanded in Evangelion: 3.0 You Can (Not) Redo, the third film of the Rebuild saga.

Although he only appears in a single episode of the original series, Kaworu significantly alters the narrative, in particular Shinji's character, and proved popular with audiences and animation enthusiasts, topping popularity polls. An ambiguous character by design, Kaworu's nature both narratively and thematically has been widely debated, and he polarized critics, with some disliking his ambiguity and the romantic undertones of his relationship with Shinji, while others praised his personality, finding him to be open, affectionate and sociable. His prominent role in Evangelion 3.0 also attracted attention, with reviewers generally appreciating his relationship with Shinji. Merchandise based on Kaworu has been released, particularly action figures.

Akio Satsukawa, a screenwriter who contributed to writing for the series' twenty-fourth episode, "The Beginning and the End, or 'Knockin' on Heaven's Door'", chose Kaworu's name. He opted for the surname Nagisa (Japanese for "shore") as a homage to Japanese director Nagisa Ōshima. The choice of a term related to the sea allowed him to connect to the names of other series' characters inspired by Imperial Japanese Navy ships and nami (波; lit. "wave") in the surname of Rei Ayanami. The name Kaworu was not written with the contemporary spelling カオル (Kaoru) with the katakana オ (o), but with the archaic character ヲ (wo). The kanji nagisa (渚) was chosen for its connection with the katakana shi (シ) and the kanji sha (者), a detail referring to the Japanese title of the episode: "The Final Messenger" (最後のシ者, Saigo no shisha). Satsukawa then created a pun with the phoneme shisha, which can mean "messenger" (使者) or "dead" (死者).

Two years before the series began broadcasting, Gainax published a presentation about the series entitled New Century Evangelion (tentative name) Proposal (新世紀エヴァンゲリオン (仮) 企画書, Shinseiki Evangelion (kari) kikakusho). Kaworu was originally going to appear in the twenty-second episode of the series as a "bishōnen constantly accompanied by a cat". Nerv would have allowed the boy to enter its laboratories and, after a clash in which his fellow pilot Shinji Ikari found himself "in the dilemma of having to fight against an anthropomorphic enemy", "the greatest secret of the organization" would be revealed. In the first drafts, the Angel would have been a cat controlling a boy; however, this idea was abandoned, and elements of it were merged into Kaworu. In preliminary proposals, he had an organ characteristic of Angels named core and the ability to modify his appearance through metamorphosis, ideas which were set aside during the series' production.

Anno conceived him as an "ideal male". According to him, "The plan was that the 'unconscious Shinji' would be Ayanami Rei, the Shinji who appears on the surface would be Ikari Shinji, and the 'ideal Shinji' would be Nagisa Kaworu". Character designer Yoshiyuki Sadamoto conceived him as "more elegant and more refined" than Shinji, and compared to him he would be "taller, thinner and with a smaller face". For the somatic features of his face, he decided to combine those of Rei, Shinji, and Asuka Langley Soryu. While designing him, Sadamoto envisioned him with a "younger" voice than in the final version. In one of the drafts of the twenty-fourth episode, he is described as a blond-haired boy, but during production staff decided to change his hair colour to white. Following a personal request from the director, colorist Harumi Takaboshi made his eyes red to be analogous with Rei's and give him "a distinct impression". Although he was conceived to appear only in the final episodes, during the making of the opening theme the main staff decided to depict him with a sketch by Sadamoto; in the editing phase, the sketch was inserted before a frame depicting Rei Ayanami and the caption "Angels".

In the early stages of production, scriptwriter Akio Satsukawa wrote some drafts of the twenty-fourth episode's script, in which Kaworu's relationship with Shinji would have been expanded upon and presented with less ambiguity. Some of his ideas included Kaworu and Shinji swimming naked in a river at night, Kaworu proposing to Shinji to play piano and cello together and a kiss scene between them. Anno originally gave him an outline that Satsukawa greatly expanded upon, something that struck Sadamoto. Though Anno did not dissuade Satsukawa and the homoerotic tone of his draft, at one point he considered it "above my tolerance level". The Evangelion staff and producers also rejected these proposals. Episode director and animator Masayuki refused to work on them and threatened to resign. The drafts underwent several modifications before being accepted as the definitive script. However, they did not change or alter the essence of Kaworu's character; Anno said the draft's "atmosphere" was preserved in the script. Anno explained he wanted to hold on to the idea of an Angel "conversing in human language", mentioning it as a progression from Shinji's conversation with the Angel Leliel in the sixteenth episode. He also considered expanding Kaworu's role in the expanded director's cut version of the episode, but decided to prioritize clarifying Kaworu's connection to Seele instead.

Staff indicated they did not expect Kaworu to provoke a strong sexual impression, nor how popular he would become. They attributed their unawareness of this to the short time they had to produce the later episodes, and mentioned that Kaworu was not supposed to hold Shinji's hand in the bath scene. This was an animation error; he was supposed to touch it instead. Like other characters in the series, Anno conceived Kaworu based on his own personality. He described Rei and Kaworu as part of his unconscious, and Kaworu specifically as his shadow—the dark and unconscious side of the psyche. According to some fans, he may have used Kunihiko Ikuhara, the director of the animated series Sailor Moon and his friend, as a model. In an interview, Ikuhara denied the rumors, comparing Kaworu's cynical personality to Anno himself, while stating he was not involved in the creation of the character. He also said he had close correspondence with Anno, with whom he was on good terms since the early design stages of Neon Genesis Evangelion. During the production of Sailor Moon, the staff went on a trip to the spa, and Ikuhara chatted all night with Anno, who also worked as an animator for some of the series' episodes. When watching the episode, Ikuhara noticed how the situation with the bath was the same as the conversation he had with Anno.