Kukun, whose real name is Mayuta, is a youthful man with a lean build who works as a label cleaner and performs as a rapper in a five-member street rap crew alongside friends Wamu, Gabi, Babo, and Hie. He lives near the apartment building of Miki Kuroda, often called Miko, and begins speaking with her after noticing her habit of planting and watering flowers. His personality is open, observant, and emotionally attentive. When Miko accuses him of only using her to get closer to Miki Makimura, he responds with an improvised freestyle rap that declares his genuine admiration for her as an individual rather than as a reflection of someone else. The sincerity of the moment moves Miko to tears, and Kukun initially worries that he has upset her, which deepens their connection. He later invites her to his home, where they exchange personal stories, and he eventually brings her to a nightclub event called the Sabbath.

Kukun is motivated by a desire to see Miko feel recognized and valued. He is drawn to her unique qualities and makes an earnest effort to show that she matters, offering her an emotional safe space she rarely finds elsewhere. He belongs to a tight-knit rap crew, and loyalty to his friends shapes much of his social world. His bond with Miko becomes his most significant individual relationship.

In the story, Kukun appears in the second episode as a friendly presence in Miko's life and reappears with her near the end of the fourth episode at the nightclub. During the Sabbath, a demon manifests nearby, and the event turns violent. Kukun is killed by the demon Silene, making him a victim of the escalating demonic conflict. His death marks a turning point for Miko, catalyzing her later transformation. After he goes missing, his rap group searches for him, unaware of what truly happened. As an ordinary human with no supernatural powers, Kukun does not undergo major internal change, but his fate illustrates the fragility of everyday life once the hidden war between devils and humans erupts. His notable ability is his talent for rap and his emotional perceptiveness, which allow him to reach others through words alone.