After losing her mother four years ago, Miki Hayakawa hopes that a move from Tokyo to the countryside with her father and younger brother will provide a quiet new start. That hope is immediately shattered upon arrival. Her eccentric father, in complete seriousness, declares their new home an independent sovereign kingdom seceding from Japan, with himself as the absolute monarch. For Miki, this means becoming a reluctant princess, and her first days at a new school become an exercise in public awkwardness as she navigates the fallout from her father's very public and very real political delusion.

Miki Hayakawa is the teenage protagonist, a girl who craves normalcy and grieves the loss of her mother, only to be thrust into the role of royalty in a one-house nation. Her younger brother is caught up in their father's whims, while the father himself is the engine of chaos, a man whose grief or midlife crisis has manifested as a grandiose, legally dubious experiment in micro-nationalism.

The story unfolds in a rural Japanese setting, a stark contrast to the anonymity of Tokyo. The primary conflict is both internal and external, as Miki struggles to build a private teenage life against the backdrop of her father's public declarations of secession. Notable narrative arcs include the initial family relocation and the shocking declaration of independence, the subsequent struggle to establish a functioning (and recognized) kingdom from a single household, and the resulting social chaos Miki endures as the local media and her curious or hostile classmates turn her into the Princess of an imaginary nation.