Every 60 years, the heavens perform the sacred ETM12 ritual that selects worthy Eto-musume to join the Eto-shin, the Chinese zodiac members. However, the original Eto-shin group has held their reign since the first ETM12, 2000 years ago, leaving no space for replacements. Nyaa-tan is an Eto-musume that represents the cat and aspires to become a member of the zodiac during the present ETM12. To achieve this, she has to win various battles using Sol/Lull, created by positive emotions of people, to obtain 12 seals- one for each Eto-shin. This task becomes challenging for her as her powers are limited compared to those of a single Eto-shin, which require a consistent energy source. Nyaa-tan's fate takes a turn with a chance encounter with Takeru Amato, who recently moved into her secret residence. Unknowingly possessing high-quality Sol/Lull, which is rare among people, Takeru becomes instrumental in Nyaa-tan's transformative journey as he helps her fulfill her dreams. In the process, they uncover the mysterious past of the Eto-shin.