Koki Murakami is a supporting character in My Dress-Up Darling, a high school student in Class 1-5 who initially appears as a quiet and unassuming classmate. He becomes a friend and eventual confidant to both Marin Kitagawa and Wakana Gojo. His background is that of an ordinary teenager attending school, but he carries a closely guarded secret: he is deeply devoted to a male host idol drama titled Council Host, a series he watches regularly with his sister. This private interest forms the core of his character, as he keeps it hidden from his peers due to fear of social judgment or embarrassment, mirroring the initial struggles of the main characters with their own hobbies.

Koki's personality is defined by a striking contrast between his external appearance and his internal nature. He has dyed short hair, a detail that might suggest an outgoing or rebellious personality, but in reality he is extremely shy, gentle, and reserved. He often tries to physically blend in by hiding behind masks, hoods, or the hood of his jacket, and he generally avoids drawing attention to himself. Despite this timid exterior, he has a passionate and earnest side that emerges only when he talks about his favorite characters from Council Host, showcasing a hidden enthusiasm that surprises those who see it.

His motivations largely center on protecting his secret fandom while enjoying it in a safe, private setting with his sister. He does not seek a major role in the school's social scene, preferring to stay on the sidelines. In the story, he serves as a classmate and friend who gradually becomes closer to Wakana Gojo after Gojo's talents in costume-making become known. His presence reinforces the series' recurring theme that people often conceal their genuine passions behind a facade of normalcy, and his quiet friendship with Marin and Gojo adds depth to the school environment.

Koki's key relationships include his bond with his sister, who shares his interest in Council Host, and his growing friendship with Wakana Gojo and Marin Kitagawa. Through these connections, he shows subtle development by slowly becoming more comfortable allowing his true interests to be known. His notable ability is his encyclopedic knowledge of the Council Host drama, which he discusses with enthusiasm when given the chance. Overall, he represents a gentle counterpart to the more outgoing personalities in the series, demonstrating that hidden interests can be a source of connection rather than isolation.