Itto Takatenjin is a first-year student at Private Tensho Academy and an energetic member of the Swimming Club. His striking appearance features voluminous red curls and vibrant lime-green eyes. He typically wears the first-year red tie, a white undershirt, dark brown pants fastened by a black belt with silver accents, and brown leather shoes, occasionally pairing this with the academy's unbuttoned black jacket.

As the Swimming Club's moodmaker, Itto displays a headstrong and socially oblivious nature, often making insensitive remarks unintentionally. His distractible focus renders his thought processes puzzling to others, yet he exhibits unexpected academic prowess, earning good grades noted by peer Ryunosuke Hanakuma. Driven by an intense passion for swimming and water, he acts impulsively—such as opening a classroom window during heavy rainfall to create an imagined indoor pool.

His closest bonds revolve around clubmates. Hozumi Uozu shares his swimming enthusiasm; their inseparable friendship shows Hozumi providing warmth after cold swims, leading Itto to view him as a caretaker. With club captain Takato Kiyosu, Itto habitually uses rude comments while omitting honorifics. He considers Minori Shido a close friend despite unreciprocated feelings and eagerly joins classmate Kai Akizuki's group activities like curry parties.

Itto briefly appears alongside fellow club members in Episode 5 ("Traumend") during an exploration of the online game Cat Walk.

His interests include candy and swimming. Documented quotes feature him declaring "I still have plenty of energy, though" to Hozumi and exclaiming "Takato! That tickles!" during an interaction with the captain.