Karen Aijō, student number 1 in Seisho Music Academy's Actor Training Department (99th Class), pursued becoming a Stage Girl after a childhood viewing of "Starlight" with Hikari Kagura ignited their promise to perform it together. This vow fueled her theatrical path, though her competitive fire only truly sparked upon Hikari's return to Japan. Raised in Tokyo, Karen trained extensively from a young age: classical ballet (2006), vocal music (2008), and modern/jazz dance (2010). She performed in Anemone Troupe productions like "Pajama Diary" (2012), "Aozora no Mukō" (2013), "Hakuryūki" (2014), and "DREAM ~ Akenai Yoru wa" (2014), securing lead roles. She chose Seisho for its challenging reputation to push toward her dream. Physically, Karen has red-ochre eyes and auburn hair styled in half-twintails with bangs swept right. She always wears a crown-shaped hairclip on her left bangs, a gift from Hikari that transforms into a full crown during revues. Her standard attire is Seisho's gray blazer uniform with a red ribbon tie. Casually, she favors denim shorts, a white T-shirt, and high-top sneakers. Her revue outfit is a blue jacket with gold accents, a red pleated skirt, black boots with gold detailing, and a red pelisse cape over one shoulder. Her weapon is the spadroon "Possibility of Youth," featuring a red gem on the hilt. Energetic, optimistic, and warm-hearted, Karen often values friendship over rivalry. Academically disinclined and initially unmotivated in morning lessons, Hikari's return reignited her training dedication, revealing latent talent and fierce determination. Her stubbornness and tenacity prove vital in revue auditions, where she consistently challenges the competitive "top star" system, advocating for collective brilliance. Her dismissive reactions to criticism or doubts are captured in her catchphrase, "Non, non dayo!" Relationships drive her growth. With Hikari Kagura, she shares a deep, fateful bond rooted in their childhood promise, though Hikari's secrecy and fear of loss cause tension, leading to a temporary betrayal during revues. As roommates, Mahiru Tsuyuzaki initially resents Karen's closeness to Hikari but, with Karen's encouragement, embraces her own worth, forming an inseparable trio nicknamed "Mamahiru." Karen supports Junna Hoshimi ("Junjun") by alleviating her fear of failure. Her friendship with Nana Daiba ("Banana") involves opposing Nana's desire to preserve the past, advocating for embracing change. Across the series and film, Karen evolves significantly. In the anime, she transforms from a passive participant into a determined revue contender, driven by her vow to stand with Hikari. After achieving their "Starlight" performance, the sequel film shows her grappling with uncertainty and lost purpose, fearing her brilliance has faded. Encouraged by Hikari, she rediscovers motivation, committing to seek new stages and challenges beyond their original dream. She consistently embodies the theme of challenging rigid systems to create a stage where all shine together. Personal trivia includes her birthday (September 27), Libra zodiac sign, fondness for umeboshi and Chinese food, dislike of green peas, and the habit of waking in cold sweats if not wearing socks while sleeping.