In the mid-21st century, Tokyo's mafia can turn into ether-enhanced Demon Lords, and Braves hunt them down. Yashiro, the Grim Reaper, reluctantly takes a new apprentice named Aki Jogamine, a high school girl training to become a Brave. He soon finds himself dragged into one troublesome case after another. The supernatural story of a scumbag master and his self-proclaimed apprentice begins!

A cat-like alien from a distant galaxy, MuMu, arrives on Earth. His goal is to learn about home appliance technology on Earth to recover the technology his species has lost. The protagonist, Sakurako, has a typical university life, but everything changes with MuMu's arrival! What begins as an unexpected cohabitation quickly turns into a whirlwind of chaotic events. The chemistry between Sakurako and MuMu leads to a super-spectacular, appliance-filled, and cat comedy adventure.