Koume Jinguji begins as the affluent grandmother of protagonist Amika, living on a secluded private island. Her death triggers pivotal shifts in Amika's life. Soon after, Amika's mother delivers a baby girl confirmed as the reincarnation of the deceased grandmother. This infant possesses an identical physical appearance and behavioral traits to the elder Koume, formally inheriting her name: Koume Jinguji.

Despite her infant body, this reincarnated Koume exhibits the distinct personality and mannerisms of her former self. Her consistent embodiment of the grandmother's characteristics generates ironic situations within the family. The story delves into the consequences of this reincarnation, centering on the evolving interactions between the infant Koume Jinguji and her older sister, Amika.

Alternative names linked to the character include "Nopiruniangniang" and "Yone-san." Another character, Ume Jinguji, appears briefly in episodes 1 and 47; the precise relationship between Koume and Ume remains undefined within the provided details.

Her background encompasses a previous existence as a formidable matriarch ruling her isolated island domain. Her rebirth into the very family she once led introduces intricate interpersonal dynamics, particularly with her granddaughter/sister Amika. The narrative investigates how her presence reshapes family bonds and influences Amika's personal development.