Kō Mukami is the second son of the Mukami household, a vampire who was originally human before being turned by Karlheinz. He was among four unrelated boys who were taken in from a bleak orphanage, where they endured harsh treatment and experimentation. Kō was repeatedly shot and injured while at the facility, and the staff paid no heed to his suffering because his patrons preferred him in a damaged state. He was near death when he was finally brought back to the orphanage, but the Mukami brothers eventually escaped together, an event that left a lasting, precious impression on Kō – the sight of the bright blue sky after their escape remains his most vivid memory.

In the human world, Kō works as an idol, a job that suits his love of attention and fashion. He is deliberately stylish, favoring pink clothing and accessories such as heart‑shaped hairpins or cat‑themed items, and he takes pride in his appearance, especially his eyes and physique. On the surface, he presents a friendly, playful demeanor, but beneath that he is selfish, two‑faced, and an extreme sadist. He uses his handsome face and charismatic idol persona to manipulate others and get what he wants, acting on a “give and take” principle. Despite his outward charm, he can be hysterical and forceful when denied what he desires, as seen when he forcibly vampirized the protagonist after she refused to give her blood.

Kō’s motivations are largely self‑centered, yet they are rooted in a deep gratitude toward Karlheinz, whom he calls the family’s “savior” for giving them a new life. He values the bond he shares with his adoptive brothers – Ruki, Yuma, and Azusa – and the protagonist, whom he affectionately calls M‑neko‑chan. To him, the protagonist is like the blue sky itself: someone precious whom he never wants to lose, and his feelings for her are distinct from his affection for his brothers. He enjoys spending time with her, teasing her, and watching her expressions, particularly when he drinks her blood from her upper arm.

In the story of Diabolik Lovers More, Blood, Kō and his brothers kidnap the protagonist Yui Komori and bring her to their mansion. They believe she is their “Eve,” and that her blood will help identify the “Adam” among them, granting the power to dominate the world. Kō’s role within the narrative is that of a captor and rival to the Sakamaki brothers, who also pursue the protagonist. His relationship with Yui is complicated – he can be cruel and demanding, but also shows a possessive, affectionate side that hints at genuine attachment.

Over the course of his route, Kō undergoes some emotional development. While his core selfishness and sadistic tendencies remain, he gradually acknowledges the depth of his attachment to the protagonist, expressing a desire to always be with her and to protect the precious “blue sky” she represents. His trust in his brothers and his gratitude toward Karlheinz also shape his growth, as he learns to balance his own desires with loyalty to his family.

As a vampire, Kō possesses superhuman speed, strength, and agility. He can control and manipulate others using his voice, and his bite can transform humans into vampires. He is a skilled fighter, relying on quick thinking and agility to outmaneuver opponents. Additionally, his idol career gives him a public platform and a network of admirers that he can exploit when needed.

Kō is a character defined by contradictions: a handsome idol who hides a ruthless, sadistic nature; a freed orphan who clings to the memory of an open sky; a selfish vampire who nonetheless holds his family and his beloved close. His journey in the series explores the tension between his self‑interest and his growing emotional bonds, all framed within the dark, melodramatic world of vampire politics and desire.