​Princess Su-ji of Nimbii—a sunlit sky realm of winged beings—defies her father's rules to investigate Nocturna, a shadowy eastern territory rumored to be inhabited by bloodthirsty monsters. Upon arriving, she discovers Nocturna is actually a peaceful, ethereal kingdom of gentle, nocturnal inhabitants. After saving a local child, Su-ji meets Prince Yoon-gi, who reveals that prejudice and isolation created the terrifying myths about his people. Inspired by their shared hope for unity, Su-ji returns home to bridge the divide between their two realms.