MuMu is a cat-like alien from a distant galaxy whose species was once highly advanced. A civil war that specifically targeted and eliminated the scientists of his kind resulted in the loss of most of their technological knowledge, leaving only the less scientifically inclined members of the species alive. MuMu survived this conflict and subsequently came to Earth with the goal of studying and learning from its household appliances, seeing them as a means to rediscover and rebuild the technology his civilization had lost. He appears before the university student Sakurako Umeyashiki in the Tokyo metropolitan area and begins cohabitating with her, an event that upends her ordinary daily life. MuMu's personality is defined by a deep curiosity about Earth's technology and a determined, persistent focus on understanding how everyday devices function. His main motivation is the recovery of his race's lost knowledge through the observation and study of human appliances, a task that he pursues systematically, often enlisting Sakurako and other humans who cross his path to assist him. As a member of his species, MuMu possesses the ability to photosynthesize, allowing him to derive energy from sunlight, and his appearance is fundamentally feline, resembling a small cat. Throughout the series, MuMu forms a close bond with Sakurako, who becomes his primary companion and host, and his presence draws in a cast of other characters, including fellow aliens who share his objective and various humans who become involved in his research. Over time, his initial single-minded focus on technology gradually expands into a broader engagement with human society and the relationships he builds, showing a degree of personal growth as he learns to navigate the chaotic circumstances his arrival creates. MuMu serves as the central figure around whom the story's comedic and educational exploration of household technology revolves, with each episode typically centering on his investigation of a specific appliance or device.