Leo Saionji, a 14-year-old student at Edel Rose Academy, was born on April 4, 2001, in Sapporo to mascot designer parents. Raised in a gender-neutral household, he frequently participated in dress-up sessions with older sisters Kirari and Yurari, absorbing their cute aesthetics without initially challenging gender norms. Elementary school bullying over his feminine demeanor and interests led to his withdrawal, sparking his sisters’ guilt for encouraging his self-expression. Determined to ease their worries, he enrolled at Edel Rose to pursue a more masculine persona.

Standing 158 cm with short pink hair and fuchsia eyes, his delicate features enhance his androgynous appearance. Shy yet earnest, he strives for self-improvement under the mentorship of Yukinojo Tachibana, whom he reveres as "Yuki-sama." Though committed to adopting masculine traits, internal conflicts over gender expression persist, gradually giving way to acceptance of his nonconforming identity through pivotal experiences in later events.

He navigates protective jealousy, particularly toward Shin Ichijo, monitoring Shin’s interactions with peers like Louis Kisaragi and awaiting his return home to assess potential romantic ties. A skilled designer, he crafts all solo outfits for his group Septentrion and excels at baking sweets. His Prism performances showcase songs such as "Twinkle Twinkle" and "Lion Heart Flower," highlighted by mid-show Prism Changes that transform his attire.

Named "Leo" for the lion-hearted strength his parents wished him to embody, he idolizes Prism Star Otoha Takanashi and collaborates with Yuu Suzuno on covers like "ALIVE." His journey weaves reconciliation between upbringing, societal pressures, and authentic self-expression, culminating in confidence to live beyond rigid gender expectations.