Miyu Kouzuki, a high school student, is sent to live with her grandparents in the countryside after her parents relocate to the United States for work. Her life takes an unexpected turn when her grandparents leave for India, and she is left in the care of their neighbor, Kanata Saionji, a young man who lives alone with his younger brother, Wanya. Kanata is revealed to be harboring a secret: he is the guardian of an alien baby named Ruu, who was left in his care by Ruu’s parents, intergalactic travelers. Miyu reluctantly becomes involved in caring for Ruu, forming a makeshift family with Kanata and the alien child.

The narrative revolves around the daily lives of Miyu, Kanata, and Ruu as they navigate the challenges of keeping Ruu’s existence a secret while managing their own personal growth and relationships. Ruu’s alien nature introduces comedic and fantastical elements, such as his ability to communicate telepathically and his advanced technological gadgets, which often lead to chaotic situations. Despite these challenges, the trio develops a strong bond, with Miyu and Kanata gradually growing closer as they share the responsibilities of raising Ruu.

The story also explores the dynamics of Miyu’s school life, where she befriends classmates like Asami and Aoi, who occasionally become entangled in the trio’s adventures. Kanata’s aloof and mysterious demeanor contrasts with Miyu’s more grounded and responsible personality, creating a balance in their partnership. Over time, their relationship evolves from one of mutual tolerance to genuine affection, though their romantic feelings remain subtle and understated.

As the series progresses, the narrative delves into Ruu’s origins and the broader implications of his presence on Earth. Encounters with other aliens, including Ruu’s parents, add layers of complexity to the story, blending slice-of-life moments with science fiction elements. The series maintains a lighthearted tone, focusing on themes of family, friendship, and the unexpected ways people come together to support one another. Through its blend of humor, heartwarming moments, and occasional sci-fi intrigue, the story captures the essence of finding belonging in unconventional circumstances.