Ruby Hoshino
Ruby Hoshino |
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| Kanji | 星野 瑠美衣 |
| Rōmaji | Hoshino Rubii |
| Age: | 18 |
| Birthday: | Unknown |
| Height: | 158 cm (5’2″) |
| Voice Actor | |
| Japanese | Yurie Igoma |
| English | Alyssa Marek |
Ruby Hoshino (星野 瑠美衣, Hoshino Rubii), more commonly referred to as Ruby (ルビー, Rubī), is the female protagonist and one of the titular characters of Oshi no Ko. She is the daughter of idol Ai Hoshino and the twin sister of Aqua Hoshino. In her previous life, she was Sarina Tendouji, a terminally ill girl who idolized Ai and was under the medical care of Gorou Amamiya. After her death, Sarina was reincarnated as the daughter of the very idol she loved, leading to a joyous new beginning she never thought possible.
Ruby’s new life initially brings her happiness and purpose, but that bliss is shattered when she witnesses her mother murdered by an obsessed fan. In the wake of Ai’s death, Ruby becomes determined to revive her mother’s dream, aiming to become a top idol herself. Over time, her motivations deepen and darken as she learns more about the tragedy that shaped her life, including the identity of her brother’s former self and the person responsible for both Gorou and Ai’s deaths. Her once pure-hearted ambition slowly gives way to a ruthless resolve, making her one of the most complex and evolving characters in the series.
Background

Appearance in anime
In her first life, Sarina Tendouji was a sickly girl confined to a hospital due to a terminal illness. Isolated and emotionally neglected by her parents, she found comfort in watching Ai Hoshino, the vibrant center of the idol group B-Komachi. Ai’s bright persona and radiant smile became Sarina’s sole source of joy and hope.
After passing away at a young age, Sarina was reincarnated as Ruby Hoshino, the daughter of Ai Hoshino, alongside her twin brother Aquamarine the reincarnation of her doctor, Gorou Amamiya. Grateful for a second chance at life, Ruby cherished her mother and quickly developed a passion for idol activities, encouraged and mentored by Ai herself. However, this newfound happiness was violently cut short when Ai was murdered by a fan shortly after a public performance.
In the aftermath, Ruby was raised by Miyako Saitou, Ai’s former manager, and continued to live with Aqua. While initially unaware of Aqua’s obsession with revenge, Ruby focuses on fulfilling Ai’s dream by becoming an idol, eventually reforming B-Komachi with the help of new friends.
Appearance
Ruby is a slim teenage girl with long, flowing pink hair, often styled in twin tails or loosely down, closely resembling her mother Ai. Like her mother and brother, she has star-shaped pupils, a visual trademark symbolizing her idol lineage. Her sparkling red eyes and bright expressions emphasize her energetic and passionate nature.
As an idol, Ruby wears elegant and colorful costumes with hearts and star motifs, embodying the same charm that once defined Ai’s stage presence. Offstage, she typically wears school uniforms or casual clothing, always maintaining a stylish and youthful look.
Personality
Ruby is initially portrayed as cheerful, optimistic, and determined, driven by her admiration for Ai and her desire to honor her mother’s legacy. She is sociable, energetic, and full of enthusiasm for becoming an idol traits that mirror her past life’s longing to be seen, loved, and accepted. Ruby’s love for the idol world is deeply genuine, and she throws herself into training and performing with admirable focus.
However, beneath her bright persona lies deep emotional trauma. Ruby represses the pain of Ai’s death and the memories of her previous life, only beginning to confront them as the truth behind their shared past begins to unravel. As the series progresses, she undergoes a significant transformation becoming more cunning, emotionally hardened, and willing to resort to manipulation or morally gray tactics to achieve her goals.
Despite her descent into darker territory, Ruby’s core remains rooted in love for Ai, for her brother, and for the life she wants to build. Her character arc explores how grief and ambition intertwine, and how the desire to protect a legacy can sometimes lead to obsession.
Role in the Story
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Idol Aspirations
After Ai’s death, Ruby becomes obsessed with carrying on her mother’s dream. She aspires to become an idol not only to honor Ai but also to shine brightly enough to prevent anyone from forgetting her. She eventually reforms B-Komachi, recruiting Kana Arima and Mem-cho as group members, and begins training and performing under the guidance of Strawberry Production. Ruby’s idol career begins slowly but gains traction thanks to her charisma, work ethic, and the emotional resonance of her performances. She often acts as the energetic heart of B-Komachi, lifting the spirits of those around her and drawing attention from the entertainment industry. -
Learning the Truth
While Aqua secretly pursues revenge, Ruby initially remains unaware of his motives and the full truth about their past lives. When she later discovers that Gorou Amamiya, the doctor she adored in her previous life, was murdered by the same man who killed Ai, Ruby’s worldview shatters. This revelation drastically alters her trajectory. She becomes more fixated on finding the culprit and willing to use fame and media attention as weapons to draw them out. Her idol career becomes a means to an end no longer just a tribute to Ai, but a tool for uncovering and confronting the truth.
Relationships
Aqua Hoshino (Aquamarine)
Her twin brother and the reincarnation of Gorou Amamiya. Though Ruby deeply loves Aqua, their relationship becomes strained over time as he keeps secrets and distances himself emotionally. She is unaware of his past identity for most of the series, and their diverging goals idol vs. revenge create emotional conflict.
Ai Hoshino
Her mother in her new life and idol in her past one. Ruby idolized Ai and was devastated by her death. Her entire career as an idol is inspired by Ai’s legacy, and she constantly seeks to be worthy of her mother’s name.
Kana Arima
Ruby’s close friend and fellow member of the new B-Komachi. The two develop a sisterly bond, supporting each other through the challenges of the entertainment industry.
Mem-cho
An older social media influencer who joins B-Komachi. Mem-cho acts as a big sister and mentor figure to Ruby, offering guidance and grounding her when she loses sight of herself.
Miyako Saitou
Ai’s former manager who takes in Aqua and Ruby after Ai’s death. Though often exasperated, Miyako cares for Ruby deeply and supports her idol career.
