Keiji Takeda is a third-year student at Shinyo Academy who serves as an initial point of view for the story. He is the boyfriend of Touka Miyashita, which places him in a unique position when he discovers that she harbors another identity within her: the enigmatic entity known as Boogiepop.

In terms of background, Keiji is depicted as a fairly ordinary young man in appearance, with no particularly distinguishing physical features, allowing him to blend into his school environment. What sets him apart from his peers is his clear and decisive vision for his future. Unlike the majority of students at the academically rigorous Shinyo Academy, who are consumed by the pressure of university entrance exams, Keiji has no intention of continuing his education. His father owns a design company, and Keiji has already secured a position there after graduation, opting to enter the workforce directly as a designer. This assured path makes him an outlier among his classmates, who often regard him with a mixture of envy and contempt for his lack of academic stress, though he remains largely untroubled by their opinions.

Personality-wise, Keiji is characterized by his calm, thoughtful, and dependable nature. He is described as clear-minded and shows little of the hesitation or existential doubt that plagues many other characters. Despite his own stable footing, he is deeply caring and loyal, particularly towards Touka. Their relationship is complicated by school rules that prohibit dating, so they communicate through a secret sign language and meet discreetly. Keiji is also notably honest and possesses a strong sense of moral observation. He is not personally involved in the supernatural conflicts that arise, but he provides a grounded human perspective on them.

Keiji's core motivation shifts from navigating a secret romance to understanding and protecting the well-being of his girlfriend, both as Touka and as Boogiepop. He becomes deeply invested in the entity that shares Touka's body, not out of a desire for adventure, but from a place of genuine concern and burgeoning friendship.

His primary role in the story is that of a witness and a confidant. He is the first person to encounter Boogiepop directly and, more significantly, becomes the entity's first and only true friend. Their meetings on the school rooftop become a regular occurrence, where they engage in discussions ranging from the nature of evil to philosophical debates. Keiji provides Boogiepop with a connection to ordinary humanity, and in turn, Keiji finds himself admiring Boogiepop's unflinching courage and willingness to speak uncomfortable truths, qualities he feels he himself lacks. He often serves as a narrator, guiding the audience through the strange events as an everyman anchor amidst chaos.

Regarding key relationships, the most important is his connection with Touka Miyashita and Boogiepop. He cares deeply for Touka, but his friendship with Boogiepop is a unique and profound element of his life. He respects Boogiepop not as an alternate personality or a mental illness, but as a distinct and admirable individual. Before her death, Keiji was also good friends with Naoko Kamikishiro, another student in a secret relationship, finding a sense of peace in their conversations that he couldn't find with male friends. He was also the object of affection for fellow student Kei Niitoki, who confessed to him; he rejected her gently for Touka, and they remained on friendly, if slightly awkward, terms.

In terms of development, Keiji begins as a young man with his future already planned, yet he undergoes an emotional journey through his interactions with Boogiepop. Initially worried that Boogiepop is a sign of mental distress in Touka, he evolves to accept the entity as a separate friend. By the end of the Manticore incident, he has come to treasure Boogiepop's company, even desperately asking him to stay when he announces he must disappear. This loss solidifies his understanding that his role, and Touka's, is to live their lives, to laugh and exist in the world that Boogiepop protects. His path is already set towards becoming a designer, and he pursues this with focus, but his perspective on the world is forever altered by his quiet friendships with two beings sharing one body.

Keiji possesses no supernatural or notable physical abilities. His strengths are entirely human: emotional intelligence, dependability, a calm demeanor, and a clear-headed perspective that allows him to accept extraordinary circumstances without losing his sense of self. He is notable precisely for being an ordinary person who chooses to offer friendship and understanding to something far beyond the ordinary.