A shy college student named Sakurako Umeyashiki has just moved to Tokyo from the countryside and is struggling to make friends. Her lonely, ordinary life is upended when a small spaceship crashes into her apartment. The pilot is MuMu, a cat-like alien from a distant world whose civilization destroyed itself in a war that killed off all its scientists and engineers. Now only the foolish members of his race remain, and MuMu has come to Earth with a desperate plan: to study everyday household appliances like microwaves, refrigerators, and vacuum cleaners. He believes these common devices contain the secrets to rebuilding his people’s lost technological knowledge.

There is just one problem. MuMu is a cat. He has no opposable thumbs, he is not particularly bright, and his favorite activity is taking apart Sakurako’s appliances without having the slightest idea how to put them back together. What begins as an unexpected cohabitation quickly turns into a daily crisis of broken electronics and feline chaos. MuMu’s destructive tendencies force the anxious Sakurako out of her shell. When she needs help reassembling her refrigerator after MuMu dismantles it, she seeks out a group at her university called the Home Regeneration Study Group. This club of eccentric students who love tinkering with appliances becomes her first real social connection, helping her make friends for the first time in Tokyo.

The conflict deepens when another alien from MuMu’s homeworld arrives. This one is named Decimal, and unlike MuMu he sees humans as an inferior species. Decimal is interested in Earth’s infrastructure rather than its appliances, and his presence brings a more serious tension to the story. Other characters include Akihiro Tsurumi, an animal-loving handsome classmate who becomes fascinated by the cat-like aliens; Miwa Samezu, a fashion-conscious student with feelings for Akihiro; and Wataru Tenkubashi, the eccentric leader of the Home Regeneration Study Group.

The narrative balance shifts between lighthearted educational comedy and science fiction adventure. Early episodes focus on MuMu’s trial-and-error experiments with specific devices, teaching both Sakurako and the reader about how microwaves, vacuum cleaners, rice cookers, and batteries actually work. As the story progresses and more aliens arrive, the stakes escalate. A radical alien faction appears, secret government agents begin monitoring the extraterrestrial activity, and the conflict eventually builds toward a potential apocalypse. The story incorporates real locations in Machida City, Tokyo, where Sakurako attends university, grounding the bizarre premise in a recognizable contemporary setting. By later arcs, the fate of Earth hangs in the balance, forcing Sakurako, MuMu, and their growing circle of friends to confront threats that extend far beyond broken refrigerators and lost friendships.