Dai Takabayashi is a fourth-grade student at Saint Terejia Gakuen and one of Licca Kayama's classmates. He belongs to the ancient Takabayashi family and resides in a crowded household with his parents, three sisters, three brothers, his grandmother, his sister-in-law, and his parents. This busy environment necessitates chores, especially running errands to the market after losing games of Rock-Paper-Scissors. While his family relationships are generally normal, he finds his strict grandmother particularly intimidating.

Academically, Dai struggles with subjects like math and shows limited interest in studies, exemplified by once mistakenly believing Antarctica was the hottest place due to its southern location. Football excites him, though mornings do not. His personality blends cheekiness and occasional aggression with underlying loyalty. He frequently quarrels with Licca, a dynamic of constant bickering coexisting with genuine friendship and mutual concern. Despite his rough exterior, he demonstrates protectiveness toward Licca and their friends when danger arises.

Secretly, Dai harbors a crush on Licca, fueling jealousy toward her affection for the older college student Rui Makiyama. This jealousy surfaces as competitiveness or irritation when Licca interacts with Rui. Conversely, he remains unaware of the romantic feelings Sumire Shinohara, Licca's best friend, persistently holds for him. His interactions include a contrasting dynamic with the studious Tomonori Michitani.

Midway through the series, Dai receives a blue Calling Ring bracelet, becoming the designated controller of Doll Isamu, the third Doll Knight. This role connects to his narrative function as Licca's "prince" within the Doll Kingdom context. The bracelet allows him to summon Doll Isamu—a swordsman knight—during threats, typically by reciting the spell "Pereso Perese Burune Buraine." This responsibility aligns with his role in protecting Licca, particularly after Doll Isamu's initial role as an antagonist under Devaul's control and subsequent Heel–Face Turn.

In the movie *Licca-chan Zettai Zetsumei! Doll Knights no Kiseki*, he actively participates when Licca and friends face danger during an amusement park outing involving the reawakened witch Dana. While the Doll Knights confront the primary threat, Dai helps address other dangers alongside the human characters.