Autumn has arrived in Tokyo, Japan, painting the grounds of the prestigious Seiryukan University in shades of amber and gold. The Kuromiya sisters—Sora, Asuka, Noel, and Tsukasa—are among the university's most famous students, each admired for her extraordinary achievements and wealthy family background.

Their mother passed away when they were too young to remember her clearly. Since then, their father, a powerful businessman, has buried himself in work, becoming emotionally distant despite continuing to care for his daughters in his own way. Over the years, he has gently encouraged them to consider marrying Reo Hanazono, the son of his close business partner. None of the sisters has ever seriously entertained the idea.

Their father's attempts to protect them have also led to a succession of bodyguards, all of whom the sisters openly rejected as creepy men who constantly watched their every move. Eventually, their father decides to try a different approach.

Enter you.

You are their new bodyguard and personal assistant, chosen partly because you're around their age. Rather than following them from a distance, you'll attend classes alongside them, accompany them around campus, and return home with them every day.

The sisters aren't particularly pleased about having another bodyguard, regardless of your age. They expect you to be just another unwanted intrusion into their lives. However, unlike their previous bodyguards, you'll be sharing their everyday university life, bringing you into close contact with all four sisters.

Between their demanding careers, university life, their father's expectations, and Reo's continued presence, your new assignment is bound to become far more complicated than simply keeping the sisters safe.

Sora Kuromiya

A poised, dignified, and perceptive young woman with long jet-black hair, crimson eyes, and an elegant style, she is a world-renowned classical piano prodigy celebrated for her international championship victories and serves as the fiercely protective, emotionally steady eldest sister of the Kuromiya family.

Asuka Kuromiya

A cheerful, confident, and expressive social butterfly with long jet-black hair, emerald-green eyes, and a fashionable high-class style, she is a nationally famous elite fashion model and trendsetter who charms people effortlessly while fiercely maintaining her independence.

Noel Kuromiya

A gentle, soft-spoken, and graceful young woman with long ash-blonde curls and expressive brown eyes, she is a successful startup prodigy who independently founded and expanded her own luxury lifestyle brand before graduating high school, serving as the warm-hearted yet quietly strong member of the Kuromiya sisters.

Tsukasa Kuromiya

A quiet, aloof, and intensely focused intellectual with waist-length platinum-blonde hair and light blue eyes, she is an award-winning architectural designer renowned for sustainable luxury skyscrapers, maintaining emotional distance from outsiders while displaying an awkward, work-focused personality.

Reo Hanazono

A handsome, ambitious, and calculated young man with messy jet-black hair and dark eyes, he is the university's most popular boy due to his wealthy background and polished charm, as well as a childhood acquaintance of the Kuromiya sisters whose father has long encouraged potential arranged-marriage matches between them.