Kaoru Kaidoh, a second-year student and tennis team regular at Seishun Academy (Seigaku), stands 173 cm tall with a lean build and notably long limbs that grant him extensive court reach. He is almost always seen wearing a bandana, typically green in the anime, and makes a distinctive "fshuuuu" sound while exhaling, earning him the nickname "Viper" or "Mamushi." This moniker irritates him when used by rivals like Takeshi Momoshiro. Despite his intimidating exterior, Kaidoh harbors a soft spot for animals, attempting to play with Ryoma Echizen's cat, Karupin and rescuing a puppy during the Nationals. He is surprisingly sensitive, easily moved by emotional speeches and prone to blushing when praised. An often-overlooked aspect is his fear of ghosts and the supernatural, highlighted in anime-exclusive episodes. His counter-puncher tennis style relies on exceptional stamina and defensive retrieval to exhaust opponents. His signature technique is the Snake Shot, a curving forehand evolved from the Buggy Whip Shot. Under teammate Sadaharu Inui's mentorship, he refines this into advanced variations: the Boomerang Snake (curving out of bounds and back in), the Short Snake (aimed behind the net player), the Reverse Snake (disrupting opponent anticipation), and the Tornado Snake (a high-speed shot with spin reducing air resistance). He also masters a version of Hiroshi Yagyuu's Laser Beam, dubbed the Gyro Laser. Kaidoh's rigorous self-designed training regimens, often exceeding Inui's programs, focus on building unmatched endurance. Primarily a singles player, he forms effective doubles partnerships, notably with Inui—dubbed the "Emerald Pair"—and later with rival Momoshiro; their competitive dynamic ultimately enhances their coordination. Kaidoh's development features significant matches. During the Tokyo District finals against Fudomine, he overcame a deficit against Akira Kamio to win 7-5, showcasing mental resilience and stamina. At Nationals against Higa Chuu in Doubles 1 alongside Inui, he imposed a strict handicap: abstaining from Snake Shots and instructing Inui not to participate, winning 6-3 alone against two opponents. This decision stemmed from a prior challenge by Rikkaidai's Yagyuu about overreliance on the technique. In the Nationals quarterfinals against Hyotei, he and Inui faced Mukahi Gakuto and Hiyoshi Wakashi; Kaidoh initially overwhelmed them with power shots to drain stamina, later unveiling the Tornado Snake to secure a 7-5 victory. His growth culminates in the series epilogue, where he becomes Seigaku's captain as a third-year, with Momoshiro as vice-captain, indicating a mellowed rivalry. Background details note he lives with his parents and younger brother, bearing a strong resemblance to his father. As a child, he cried frequently and was often mistaken for a girl in kindergarten, leading to being dressed in skirts. His hobbies include marathon running and collecting bandanas. Favorite subjects, foods, and colors are noted, alongside his family members' names and ages, adding layers to his character beyond tennis.