Kyosuke Kasuga is the main protagonist of the series. He is a transfer student who has just moved to a new town with his family, a circumstance born from necessity rather than choice. The eldest son of the Kasuga family, he and his younger twin sisters, Kurumi and Manami, are espers who possess a range of psychic abilities. The family has a strict rule against using these powers in public, as being discovered would force them to relocate once again. This history of constant moving has made Kyosuke particularly anxious about maintaining their secret, and he frequently nags his sisters to be more careful.

On the surface, Kyosuke appears as an ordinary, somewhat unremarkable high school student. He is kind-hearted, gentle, and possesses a strong sense of justice, often rushing to help someone in trouble. However, his most defining characteristic is his profound indecisiveness. This flaw is the primary engine of the story's central conflict. Kyosuke falls deeply in love with the beautiful and mysterious Madoka Ayukawa at first sight, but before he can act on his feelings, he finds himself pursued by Madoka's cheerful and innocent best friend, Hikaru Hiyama. Instead of clarifying his true feelings, Kyosuke becomes trapped in a complicated love triangle, unable to reject Hikaru for fear of hurting her and unwilling to abandon his hopes for a relationship with Madoka. This leads him to behave in a cowardly and two-timing manner, such as using his powers to date both girls simultaneously, an act that would later cause significant guilt and turmoil.

Beyond his romantic struggles, Kyosuke is often the straight man to the antics of his perverted friends, Hatta and Komatsu, and his mischievous sisters, frequently becoming a comedic victim of circumstance. He is not particularly gifted academically, often scoring near the bottom of his class, which contrasts sharply with the brilliant Madoka. Despite this, he has a hidden talent for photography, having assisted his father, a professional photographer, and this skill eventually points him toward his future career path. He is also noted to be weak to alcohol, leading to embarrassing situations when he drinks.

Kyosuke's psychic powers are a key part of his identity, though they are typically used for mundane or selfish purposes rather than heroic feats. His abilities are extensive and include telekinesis, teleportation, precognitive dreams, time travel (often triggered by falling down stairs), hypnosis, and temporarily enhancing his physical abilities. While he is extraordinarily powerful, he primarily uses these gifts for personal convenience, like teleporting between dates or rewriting a menu, which often backfires and creates more problems than they solve. The powers serve as both a narrative tool for comedy and a source of dramatic tension, as their use constantly threatens to expose his family's secret.

His primary motivation throughout the series is to resolve his feelings for Madoka without destroying his friendship with Hikaru. His character development is a slow, often frustrating process of growing a backbone and learning to take responsibility for his actions. The story culminates in Kyosuke finally choosing Madoka, a decision that requires him to confront the pain he has caused Hikaru and accept the end of their established dynamic. In later films set after the main series, Kyosuke matures into a young adult, pursuing a career as a photographer, a path that allows him to channel his sensitivities into a profession defined by observation.