Leo Saionji trains as a Prism Star at Kakyoin Academy's Edel Rose division. Standing 158 cm tall with a small frame, he has pink neck-length hair and fuchsia eyes that often draw feminine first impressions. Born April 4, 2001, in Sapporo, his family includes parents Hirika and Non Saionji and older sisters Kirari and Yurari. His name "Leo," meaning "lion" in Latin, embodies his parents' hope for his inner strength.

Raised in a gender-neutral home by mascot-designer parents, Leo regularly wore feminine clothing and played dress-up with his sisters, initially unaware of gender distinctions. Elementary school bullying over his appearance led to his withdrawal. Blaming themselves for his femininity, his sisters' guilt motivated Leo to enroll at Edel Rose, seeking to become "masculine" to ease their worries.

Leo idolizes kabuki-trained Yukinojo Tachibana as a mentor for insights into femininity and masculinity, though his attempts to emulate Yukinojo's guidance rarely succeed. Shy and clumsy, he adores cute aesthetics and exhibits jealousy when Shin Ichijo interacts closely with others like Louis Kisaragi or female friends, even monitoring Shin's activities and scent after outings.

Performing under the "Lovely" brand, Leo specializes in songs such as "Twinkle☆Twinkle," "Peach-colored MAX Jump!," and "Surprise Decoration!" He executes "Prism Change" outfit transformations mid-performance and signature Prism Jumps like "Metamorphosis of Love and Mystery" and "Lion Heart Flower." He designed all solo outfits for group Septentrion and Taiga Kougami's Prism King Cup attire.

Leo admires Prism Star Otoha Takanashi, covered the duet "ALIVE" with Yu Suzuno, and crafts sweets skillfully. His journey culminates in "Shiny Seven Stars," where he embraces his gender-nonconforming identity, regaining confidence to express himself authentically beyond conventional masculinity.