TV-Series
Description
Kaoruko Kazuki is a central figure in the second season of the anime BBK/BRNK, known as Hoshi no Kyojin, and is the long-lost twin sister of the protagonist, Azuma Kazuki. Physically, she is a teenage girl with distinctive blue hair cut to neck-length and yellow eyes. As a child, Kaoruko lived with her family, including her mother Migiwa, on a floating island called Treasure Island, where she and her brother were surrounded by the giant, sleeping beings known as Buranki.

In her youth, Kaoruko was portrayed as a determined and emotionally driven child. Desperate to find a cure for her mother's mysterious illness, she took a reckless action, managing to activate the giant Oubu. This act had the unintended and catastrophic consequence of awakening numerous Buranki, forcing her mother to step in to protect the family, a situation that suggested a great personal sacrifice. This traumatic event led to a separation; after she and her brother were sent away from the island, Kaoruko ended up in Taiwan and has held a deep-seated grudge against Azuma for leaving her there.

Kaoruko's personality in the present is a dramatic contrast to her brother's modest and mild-mannered demeanor. She is loud, obnoxious, and a self-described large ham, often being the most bombastic and theatrical character in the cast. Upon reuniting with Azuma, she rejects him vehemently, calling him stupid, smelly, and useless, and treats him as a stranger due to what she perceives as his abandonment of her. Even when her brother comes to her rescue, she can be ungrateful, demonstrating the deep well of sibling rivalry and trust issues that define their initial interactions.

Her primary motivation in the story is driven by a mysterious figure known as Monsieur Guy. Under his guidance, she possesses a powerful black Oubu heart and leads her own team of Buranki limbs, which are on loan to her. Her role is initially that of an antagonist, as she reveals that she manipulated some of the key events that transpired in the first season. Her ultimate goal is to confront her brother and his companions, demanding that they hand over Oubu's heart, which leads to a direct and emotional clash between the twin heart-users and their respective teams. Her relationship with Azuma is the core of her development, moving from a place of deep resentment and a desire for rivalry to a more complex dynamic as the reasons for their separation come to light.

As a Buranki heart user, Kaoruko has the notable ability to pilot and control a giant Buranki, using her team's limbs in battle. Her talents in this area were evident even in childhood, where she appeared to be the more naturally gifted of the two siblings. Throughout her confrontation with Azuma, her powers and capabilities as a rival heart user are showcased, forcing her brother to fight at full strength.