Rina Yuuki is the daughter of famous actress Shizuka Yuuki and becomes Hiroshi Houshou's stepsister after their parents' marriage. Her absent biological father is replaced by stepfather Ken Houjou. She works as a popular, beautiful idol singer with a substantial public following, performing in studios and major venues like Yokohama Dome. Her career includes public appearances such as press conferences addressing her family's new structure and recording songs like "Magical Kiss."

Initially, she fiercely opposes the new family arrangement, particularly Ken's concealment of Hiroshi's existence. She publicly rejects Hiroshi as her brother by disrupting a press conference with a simulated armed protest using a toy machine gun. Her hostility extends to home life, where she throws objects when Hiroshi accidentally intrudes on her changing. She also objects to Ken assigning Hiroshi as her attendant for idol activities.

Her relationship with Hiroshi shifts through shared experiences. After witnessing his support for novice idol Chisato Miura during her debut performance and his dedication to transporting Rina via borrowed bicycle despite illness to prevent a concert delay, she acknowledges him as "onii-sama." She expresses gratitude by attempting to cook for him during his recovery, symbolizing acceptance of their sibling bond.

Domestically, she initially handles household cooking before Hiroshi's arrival, though her meals are unpalatable. Her personality merges public poise with private volatility, reacting fiercely to privacy breaches but showing concern for Hiroshi during his illness. She occasionally displays playful mischief, like orchestrating a prank involving exploding flowers meant for her.

Her character design includes moments of partial nudity during accidental walk-ins, featuring distinct undergarments in these scenes.