Momo Miyaura, an introspective 11-year-old, faces profound change after her father Kazuo’s sudden death. Uprooted from Tokyo to a secluded Seto Inland Sea island with her mother Ikuko, she wrestles with grief and isolation in an unfamiliar world. A letter from Kazuo bearing only the salutation *"Dear Momo"* torments her, its incomplete message fueling anguish over their fractured final conversation—a quarrel about his absence at a promised event.

Retreating into solitude, Momo rebuffs friendships with island children like Yota and Umi, her guilt over Kazuo’s death hardening into emotional barriers. Tensions simmer with Ikuko, who masks her sorrow to uphold normalcy, straining their fragile dynamic.

Her transformation unfolds upon encountering three mischievous exiled deities—Iwa, Kawa, and Mame—invisible to others but relentlessly present in her life. Though initially disruptive, their antics gradually draw Momo out, compelling her to voice buried regrets and confront her fraught relationship with Ikuko. A climactic argument triggers Ikuko’s near-fatal asthma attack, thrusting Momo into a storm-lashed race for aid. This desperate act bridges their divide, sparking mutual acknowledgment of shared grief.

Healing culminates during a communal memorial rite, where Momo interprets Kazuo’s unfinished letter as an unspoken testament of paternal pride, dissolving her lingering shame. Embracing her island life, she joins Yota and Umi’s activities, signaling newfound openness. The three spirits depart once their task concludes, their exit underscoring Momo’s restored bonds with family and community.

Noted for her petite frame, brown hair, and eyes, Momo frequently wears a pink shirt—a quiet nod to the meaning of her name.