Kei Miyama is a member of the hip-hop group 1Nm8, where he serves as the leader and rapper under the MC name 7. He has pale orange hair with an asymmetrical fringe and grey eyes with orange highlights. His typical attire includes a white double-layer hoodie bearing the 1Nm8 logo on the right sleeve, white pants with rolled cuffs, and plain white sneakers. He is often seen wearing wireless earbuds and a silver bracelet known as the Innocence Bangle, which is his phantometal accessory.

Kei is described as a genius with an overwhelming degree of sensitivity toward sound. Making music comes to him as naturally as breathing, and he has little concern for anything outside of music. He has few other interests and tends to be detached from everyday matters. However, in his own way, he does care for his fellow group members Itsuki and Rokuta, though he often shows this care indirectly.

Before joining 1Nm8, Kei was the center of the idol group VISTY at the peak of their popularity. He left the group due to personal reasons, driven by a desire to bring something to an end with his own hands. This decision marked a turning point in his life, leading him to form a new group with Itsuki and Rokuta, with whom he now lives under one roof. His past trauma is tied to the sudden disappearance of his little brother, a muddy stream of sound, and a sad melody.

In the story of Paradox Live The Animation, Kei’s role is that of a former idol turned underground rapper who channels his emotional experiences into his music. His notable ability is his extraordinary musical intuition, allowing him to create and perform with a natural, almost instinctive flow. He is also a Phantom Rapper, capable of generating illusions linked to his emotions through his phantometal during battles. His development centers on reconciling his past and finding a new path alongside his current team, using music as a means of expression and resolution.