Yumemi Hidaka gains the unique ability to see floating islands in the sky around age five. This isolates her from peers who cannot perceive them, causing significant childhood distress. She habitually carries a pink umbrella to block her view of the sky and avoid further alienation. Her only supporters are childhood friends Ichiko Ono and Suzume Imamura, though the friends' inability to see the islands initially strains their relationships.

Yumemi later encounters Munto, the king of the Magical Kingdom in the Heavenly realm. He seeks her help in restoring akuto—the energy flow sustaining both his world and the human dimension. Munto appears unexpectedly during her daily activities, explaining the critical depletion threatening both realms. Their initial encounters involve confusion and disbelief from Yumemi, compounded by visions of Munto's past and traumatic events like falling celestial pillars causing Earthly disasters. Her connection to Munto deepens as she experiences flashbacks of his struggles, including ostracization within his kingdom and the burden of leadership.

Yumemi evolves from passive uncertainty to proactive determination. In early encounters, she hesitates to engage with Munto, influenced by Ichiko's protective skepticism and her own self-doubt. Witnessing escalating crises, such as the near-collision of the Heavenly islands with Earth, culminates in her decision to physically reach across dimensions to aid Munto during a critical moment. This act demonstrates her newfound resolve, temporarily stabilizes the dimensional rift, but leaves her concerned for Munto's well-being.

A year and a half later, Yumemi grapples with intensified visions of Munto's injuries and the Heavenly realm's deterioration. Her concern drives her to independently investigate supernatural phenomena, like interacting with an energy-emitting sacred rock at a local shrine, which amplifies her visions. She actively seeks locations tied to previous encounters with Munto, reflecting her growing acceptance of her role. Her emotional attachment to Munto becomes more pronounced, with subtle indications of mutual affection developing.

Yumemi's family includes parents Shigeru and Nozomi Hidaka, and a younger brother named Chikara. Her home life is generally supportive, though her mother initially dismisses her concerns about responsibility as age-inappropriate. Relationships with Ichiko and Suzume remain central; Ichiko's overprotectiveness occasionally conflicts with Yumemi's increasing independence, while Suzume provides steadier encouragement regarding Yumemi's choices related to Munto.