Aone Shikimiya, the older sister of Mana Shikimiya, leads the idol unit Stellamaris as a third-year middle school student at Marehoshi Private Girls' Academy's main branch. Her charismatic talent consistently secures Stellamaris the top position in middle school idol charts. Aone balances pride in her unit's accomplishments with a genuine passion for the art of idol performance. She cherishes her family deeply, especially her younger sister Mana, openly showing affection like hugging her in public. Aone enjoys little birds and mille-feuille pastry, with no noted dislikes.

Physically, Aone has long brown hair, typically worn loose except for a section pulled back into twin tails secured by black ribbons accented with longer magenta ribbons. She features layered bangs, a prominent cowlick mirroring Mana's, and blue eyes. Her casual style leans mature with natural tones. Her primary idol outfit consists of a black lace-detailed top featuring magenta floral accents, a large back ribbon, ruffled hip adornments, and distinctive asymmetrical legwear: a white stocking with a black cuff on the left leg and full white fabric coverage on the right, paired with magenta pumps.

Aone's relationship with Mana is central to her background. Mana transferred to Marehoshi's Takao branch and initially avoided idol activities, contrasting with Aone's success. Their separation, with Mana living with an aunt, implies unresolved family dynamics. During the national Prism Stage competition, Aone's leadership of Stellamaris directly challenges Mana's unit KiRaRe. Their interactions, particularly a confrontation reviving Mana's past struggles, reveal a complex history where Aone's influence may have contributed to Mana's initial reluctance toward idolhood. Stellamaris's dominance positions Aone as both a professional rival and an emotional catalyst for Mana's growth.

Her surname "Shikimiya" combines "formula" (式) and "temple/shrine" (宮), while her given name "Aone" translates to "green/blue" (碧) and "sound" (音).