Kazuki Nishina, originating as a main character from "Pretty Rhythm: Rainbow Live," is a 16-year-old with dyed silver hair (originally black), brown eyes, and tan skin. Coming from a family of sign-artists, he works in their sign-making shop. Kazuki practices street-style Prism Shows, incorporating street dance elements, as part of a street-dancing group; this style is not officially recognized by the Prism Show Association. Known as the "Street-style charisma," he became a Prism Star inspired by former street-style Prism Star Rei Kurokawa. His personality is straightforward, warm-hearted, caring, and reliable, especially as an upperclassman.

He is the childhood friend of Kouji Mihama, Ann Fukuhara, and Wakana Morizono, though he initially remembered Wakana poorly. A key event involved Kazuki giving Ann a song composed by Kouji, leading Wakana to accuse him of theft. To resolve this, he entered a Prism Dance battle with Hiro Hayami. During the event, Kazuki injured his foot saving a child from a car, resulting in a draw. He later provided dance lessons to Ann and her friends and confronted Wakana at a summer festival, challenging her to a shooting game.

Set 1.5 years after "Pretty Rhythm: Rainbow Live," within the "King of Prism" series, Kazuki is a famous alumnus of Edel Rose Academy. There, he formed the group Over the Rainbow with Kouji Mihama and Hiro Hayami. He eventually left Edel Rose to establish a new agency. His legacy influences characters like Taiga Kougami, a street-style performer from Aomori who idolizes Kazuki and was inspired by him after moving to Tokyo.

Kazuki's background includes his birthday on May 5, blood type A, and a cousin named Naomi. His parents are not shown or identified in any media. Merchandise for "King of Prism: Dramatic Prism.1," such as a card holder and outing stick, features Kazuki's visual design based on Prism Show costumes.