Nagisa Hazuki is a male transfer student arriving at Iwatobi High School, reuniting with childhood friends Haruka Nanase and Makoto Tachibana after separation during junior high. They previously swam together at the Iwatobi Swimming Club in elementary school alongside Rin Matsuoka. Nagisa developed a deep admiration for Haruka's dolphin-like swimming grace during this time. His three older sisters frequently dressed him in girls' clothing and swapped his swimsuit with theirs, leading to an incident where Haruka lent him a suit, cementing Nagisa's lasting respect. This familial teasing persisted into high school. He possesses honey-blond wavy hair, magenta eyes, and an average, lean build with notably developed soleus muscles. His height grows from 135 cm (4'5") in elementary school to 167 cm (5'6") by university. His swimwear evolves from red jammers with yellow star patterns to black with pink designs. As a high school student, he wears seasonal uniforms: light brown trousers and a tan sweater in fall/winter, gray trousers and a sweater vest in spring/summer, with his third-year tie changing to green. Cheerful and enthusiastic, Nagisa often acts impulsively without considering social repercussions, though devoid of malice. He demonstrates tenacity in pursuing goals, notably reforming the Iwatobi High Swim Club by persuading Haruka, persistently recruiting Rei Ryugazaki after track practice despite initial refusal, and securing faculty approval. He exhibits a rebellious streak, sneaking into Samezuka Academy's closed pool to skinny-dip. Childlike tendencies include speaking with his mouth full, untidiness, playful behavior like imitating a rockhopper penguin, and stubbornly referring to Gou Matsuoka as "Gou" against her preference, highlighting his unconventional problem-solving. His specialty is breaststroke, characterized by accelerated speed after turns and an illusion of extending arms, as noted by Rin Matsuoka. He serves as the swim club's treasurer and later vice-captain in high school. Influenced by Rin, he experiments with butterfly stroke, aspiring to master all strokes for individual medley events, though he initially feels uneasy swimming alone after competing in relays. His dedication includes rigorous training camps, like swimming circuits between islands, and practicing relay techniques with Rei before tournaments. He shares close bonds with swim club members. Nagisa frequently interacts playfully with Rei, coaxing him during training and daily activities, and relies on Makoto for guidance during conflicts with Haruka. His admiration for Haruka remains central, often motivating group actions like convincing Haruka to participate in relays. He maintains a rivalry-turned-camaraderie with Rin and the Samezuka team, viewing them as friends striving toward shared goals despite school differences. Post-high school, he attends Naribusawa University, joining its swim team while continuing to value swimming with friends. Trivia includes his August 1st birthday (Leo zodiac), association with rockhopper penguins, ownership of a pink cellphone, and a sweet tooth favoring strawberry shortcake and "rock and hopping bread." He dislikes math, peppers, and onions, excels in history, and enjoys insects, horror movies, and thrill rides. His room features North American furniture designs, and he talks in his sleep.