Haruka is an adventurous young girl who organizes an expedition with friends to investigate rumors of supernatural occurrences—specifically cats transforming into spirits—within an abandoned building. During this exploration, she discovers an injured cat and assumes responsibility for its care, naming it Nyan. The cat’s true identity is subsequently revealed as Ultra Nyan, a being from the Ferris star in the Felis constellation, tasked with collecting forgotten happy energy.

Following this initial encounter, Haruka becomes Nyan's primary caretaker and owner. Their bond faces a challenge when Haruka develops a cat allergy, compelling her to temporarily entrust Nyan to a friend's home. This separation causes Nyan to lose its spirits, underscoring their deep connection. The situation unfolds amid escalating crow attacks threatening the cats' sanctuary park, occurring shortly after an incident where Nyan protected a boy named Kosuke from crows.