Kiyotaka Yoshino is the central protagonist of Da Capo III, a character whose story unfolds across two distinct yet interconnected settings: the familiar Hatsune Island and the magical Kazamidori Academy in London. On Hatsune Island, he is a second-year student at Kazami Academy living with his cousin, Charles Yoshino, and is the sole male member of the school's official newspaper club. He is described as a hardworking individual who, despite being surrounded by a group of female friends who show a clear romantic interest in him, is notably dense and oblivious to their affections. This insensitivity extends to his relationship with his cousin Charles, with whom he shares a home, often finding himself in awkward situations due to her assertive and affectionate nature, while he typically handles the cooking due to her disastrous skills in the kitchen. His primary motivation within this setting is a deep-seated desire to preserve his current, peaceful daily life, a wish so strong that he makes it upon the legendary, wish-granting sakura tree on the island.

The narrative takes a significant turn when Kiyotaka's role is revealed to be far more complex. In the main story arc set at Kazamidori Magic School in 1950s London, he goes by the name Katsuragi Kiyotaka, living as the older brother of Himeno Katsuragi. This version of Kiyotaka is a powerful wizard, a fact he conceals from most people, with only a few, like the school principal Rikka, aware of his true capabilities. His magical talent is exceptionally high, placing him as a fourth-category magician, and he possesses a refined ability to look into and even enter other people's dreams at will, a power he can control completely unlike some previous protagonists in the series. His decision to attend the magic school is ostensibly to care for his sister Himeno, but his true motivation is to free her from a binding family fate, demonstrating a strong sense of responsibility and protectiveness. He also displays remarkable creativity and power by inventing unique magical spells, including one that creates traditional Japanese sweets from the user's hands.

Kiyotaka's key relationships form the core of the story's emotional landscape. His bond with his cousin Charles is one of familial closeness and frequent comedic frustration, while his relationship with the enigmatic Rikka Morizono, the school idol who claims they were lovers in a past life, is more mysterious and central to the magical plot. His sisterly connection with Himeno, whether as a neighbor on Hatsune Island or as her guardian in London, remains a constant source of warmth and motivation. The character undergoes significant development through the revelation of his true identity. In a major twist, Kiyotaka is ultimately revealed to be the maternal grandfather of both Sakura Yoshino and Junichi Asakura, the protagonists from previous Da Capo installments. Having married Rikka, he fathered two daughters: one blonde who would become Sakura's mother, and one with black hair who would become Junichi's mother. This revelation re-contextualizes his entire journey and connects him directly to the overarching legacy of the series, establishing him as a pivotal figure in its timeline, even if he himself remains unaware of his connection to his grandchildren throughout most of the story.