Kazuki Shikimori is the male protagonist of the story and a seventeen-year-old second-year student at Aoi Academy, an elite school for magicians. In a world where a person's social standing is largely determined by the number of times they can perform magic, Kazuki finds himself at the very bottom of the hierarchy. While a typical magician can cast spells thousands of times in their lifetime, Kazuki has a tragically low limit of only eight spells before he will turn to ash and disappear. Because of this severe limitation, he is socially withdrawn at the beginning of the series, has few friends, and is largely overlooked by his peers, especially the female students who see him as undesirable.

His unremarkable status is turned upside down when it is revealed that he is a direct descendant of some of the most powerful magicians in history, from both the East and the West. This rare bloodline has fused within him, meaning that although his own spell count is low, his genetic material is incredibly valuable. It is believed that any child he fathers could become the most powerful magician in the world. Upon this discovery, Kazuki becomes the sudden and unwilling target of numerous girls at the academy who seek to secure his genes for their own families' prestige and power.

In terms of personality, Kazuki is fundamentally a good-natured, honest, and selfless individual. Despite the immense personal cost of using his precious magic, he consistently chooses to help others in need, even when doing so brings him closer to his own demise. He can be indecisive and easily flustered, especially by the aggressive affections of the girls around him, but his defining trait is his unwavering kindness and his strong sense of duty to do what is right. He places great importance on keeping his promises, a trait that shapes many of his most important relationships.

His central role in the story is that of the coveted prize at the heart of a chaotic romantic conflict. His life is drastically altered when three girls from powerful families begin pursuing him with distinct intentions. Yuna Miyama is a transfer student who claims to be his wife, reminding him of a childhood promise he made to marry her. Kuriko Kazetsubaki is the aggressive and wealthy heir to the Kazetsubaki family who openly desires his genes to produce a powerful successor. Rin Kamishiro is a stoic and reluctant swordswoman initially ordered by her family to secure his genes, though her feelings for him gradually become genuine. These three girls form the core of his relationships, and his selfless nature eventually wins over even the most reluctant of them.

Kazuki undergoes significant development as the series progresses. Initially a lonely boy resigned to his fate, he slowly becomes more courageous. His willingness to sacrifice himself for others comes to a head when he uses his last spell to save Yuna from a fatal magical illness. Instead of turning to ash, he becomes a ghost, a state that prompts the three girls to set aside their rivalry to find a way to restore him. In a unique turn of events, when he is finally restored to human form, he does not lose his memories. Instead, as a side effect, he splits into ten separate physical copies of himself, each one left for the girls who love him.

Despite his low casting limit, his magical ability is extraordinarily potent. Each of his few spells is capable of feats of nearly omnipotent power that others can only dream of, such as creating a blizzard in the middle of summer, merging buildings together, or banishing powerful otherworldly monsters. Even though he possesses the potential to be the most powerful character in the series, his true strength lies not in raw power but in his selfless willingness to use his limited and invaluable magic for the sake of his friends.