Kurumi serves as a guardian angel, reincarnated from a hamster once owned by Gorō Mutsumi. In her past life, she was born on July 4, 1988, within a litter cared for in Gorō's classroom. A childhood classmate of Gorō's, Kurumi Kimihoshi, desired to adopt her but faced parental refusal; Gorō subsequently adopted the hamster, naming her "Kurumi" after his first love interest, Kurumi Kimihoshi, honoring her bond with the animal.

This hamster learned to escape her cage but perished from starvation three days later while lost. That experience instilled a lasting fear of hunger in her reincarnated form.

As a guardian angel, Kurumi appears as a girl aged 13 to 14 years, standing 143 cm tall. Her design incorporates hamster-like traits, including a hairstyle suggesting ears and a mouth shape reminiscent of a hamster's. She is associated with the color yellow. Her personality is carefree, frequently ending sentences with "Nano." Haunted by her past death, she compulsively eats often to prevent starvation and enjoys sleeping.

She holds an Intermediate rank among guardian angels and belongs to the first group returning to serve Gorō. She exhibits profound loyalty and protectiveness towards him, though her constant eating significantly strains his finances.

Her relationships with fellow angels develop throughout the series. She shares a close friendship with Ran and maintains a generally friendly, though sometimes argumentative, rapport with Tsubasa. Initially, she clashes fiercely with Tamami, resulting in physical fights; however, their relationship gradually improves, becoming more amicable over time.

Her background meaningfully connects her to Gorō’s childhood, both through her namesake, Kurumi Kimihoshi, and the shared responsibility he and Kimihoshi held for the classroom hamsters. This history reinforces her role as a symbol of his past affections and losses.