Kanako Watanabe is a student at Southern Cross High School who, despite being only fifteen years old, is already a married woman. Her husband is Leon Watanabe, a sixty-five-year-old business tycoon who leads the powerful Grand Tonnerre financial group. The marriage is portrayed as a practical arrangement held together by mutual benefit rather than affection, with a significant language barrier between them as they communicate only through an interpreter. She lives on her own lavish luxury cruise ship, the Thunder Girl, which is permanently docked at the island's port.

In her daily life at school, Kanako projects the image of a spoiled, bored, and flirtatious young woman who is unconcerned with rules or social conventions. She often speaks out of turn during class, has her servants cut her hair in the classroom, and openly teases her male classmates. A distinctive habit is her game of kissing boys through the glass of a classroom window, a practice that serves as her unusual way of attempting to form personal connections. This behavior stems from her lack of prior schooling experience, as she had never attended school before enrolling at Southern Cross, leaving her unfamiliar with how to interact with peers in a typical manner. Her flirtatious personality is a deliberate facade that allows her to observe others while keeping her true nature hidden.

Beneath this superficial exterior, Kanako is highly intelligent, calculating, and possesses sharp business acumen. She manages substantial financial assets and investments for herself and her husband, demonstrating expertise that far exceeds her age. This intelligence is channeled into her role within the secret organization known as the Glittering Crux Brigade, where she operates under the alias The President. She leads the organization's fourth division, called the Adult Bank, which holds significant financial power and effectively claims ownership over the mystical giant robots known as Cybodies. Her own Cybody is named Betreida.

Her true motivations are not selfish but driven by a sense of responsibility and a desire for control. She joined the Glittering Crux not for power or status, but because she believed the release of the Cybodies into the world was inevitable and wanted to manage them peacefully to prevent disaster. This pragmatic and forward-thinking nature is also evident in her preparation for potential catastrophes; she keeps her large cruise ship docked specifically to serve as an evacuation vessel for the island's residents should volcanic eruptions triggered by the breaking of seals occur. She is willing to sacrifice her personal relationships and integrity for what she sees as the greater good, stating that becoming whatever person she must be is an acceptable price for achieving her goals.

Her relationships are complex and often defined by the gaps between her public personas and her genuine feelings. She shows a particular interest in her classmate Takuto, who sits in front of her, frequently singling him out for her flirtatious advances and later developing romantic feelings for him. She is also the employer of her servants, Simone and Takashi, who serve as her secretary and attendant. The relationship with Simone is especially layered, as Simone is secretly the daughter of Kanako's husband, making Kanako her stepmother despite their similar age. Simone initially resents Kanako and seeks revenge, but it is revealed that Kanako saved Simone's life after a serious accident by using a Cybody, an act that demonstrates Kanako's hidden caring nature, even if she rarely shows it openly. Despite her calculating demeanor, Kanako does care for those close to her, such as when she fretted over Simone's safety in battle or tried to discourage Takuto from fighting her because she feared killing him.

Throughout the story, Kanako undergoes significant development. Initially an antagonist aligned against Takuto, she engages him in combat but is defeated, losing her privilege as a Star Driver. Her perspective shifts as the series progresses, and by the final episodes, her previously hidden true mark manifests, allowing her to reawaken her Cybody and fight alongside Takuto against a greater threat. She lastly reveals a desire for a normal high school experience, envying her peers for their ordinary lives and relationships, which she cannot fully participate in due to her unique circumstances and weighty responsibilities. Her physical abilities are as remarkable as her mental ones; she is a highly skilled boxer capable of knocking out large, muscular opponents with just a few punches.