The ordinary Tanaka family, who loved their pet cats and lived a modest life, met an abrupt end when a major earthquake struck. They died instantly, only to collectively awaken in the bodies of an aristocratic family in a fantastical new world. Now reincarnated as the wealthy Stuart family, each member retains the full memories of their past life in Japan, even as they navigate their new roles dressed in Western-style noble attire.

The family consists of the former parents, Kazushi and Yoriko Tanaka, who are now the young Earl Leonard and his wife Melsa, both aged 35. Their three adult children from Japan have also been given younger bodies. The eldest son, Wataru (38), is now the 15-year-old George. The daughter, Minato (35), has become the 12-year-old Emma, who is the central protagonist. The youngest son, Heita (33), is now the 9-year-old William. Their beloved calico cat, Komei, has also been reincarnated, but as a giant, horse-sized magical beast with eight lives, who is fiercely protective of the family. Another companion is Violet, a highly intelligent pet spider Emma kept before regaining her memories.

The story follows the Stuarts as they apply their modern Japanese common sense and values to the customs of a medieval-level kingdom. The matriarch, Melsa, is obsessed with getting her children married, as she never had grandchildren in her previous life. George tries to maintain peace within the family. William has developed an unfortunate lolicon complex in his new young body. Emma is an airheaded but well-meaning girl whose primary obsessions are catching rare bugs and a crush on the much older king. She tends to bumble through events, creating misunderstandings that somehow work out in her favor, often to the bewilderment of those around her.

A notable early narrative arc begins when the family relocates from their rural territory to the royal capital. Here, Emma must attend a royal ball, where she deals with petty noble girls, accidentally befriends her tormentors, and becomes the unexpected center of attention. Her family sets up trade, driven by their deep craving for rice, and they discover the existence of the "Imperial Japan" empire in this world, a nation with a language and culture nearly identical to their original home, heavily implied to be founded by previous reincarnators. Emma's path crosses with Prince Tusk, who speaks this "Imperial Language," leading to a huge uproar that draws the attention of the entire country.

The narrative later shifts to a more serious arc when Emma and her family become entangled in a conspiracy involving a demonic invasion from a hostile Western Empire. The first prince returns from the west acting strangely, and the kingdom realizes he has been compromised. The Stuarts join a dangerous school field trip to a monster forest, which turns out to be a trap for an invasion. The king himself becomes involved, and Emma must use her wits to save him. The family's unique assets, including their giant cats and Violet's durable, healing thread, prove essential in defending the capital from cannon fire and powerful monsters. Despite the growing threat of war, the family continues to approach their otherworldly life with a blend of confusion, resilience, and a desire for a peaceful, modest existence, much like the one they left behind.