The Mukai siblings, Sunao and Ai, were having a normal day, when suddenly, a space ship suddenly fell into the yard of their house!? What came from within the ship was a little girl who called herself Yurumi. "We're from the cosmic repair shop, 'Rutsubo Mechanic Company,'" said another girl, Yurumi's partner, Shimeru, who stepped out afterwards. And so, in the Mukai household, a comedy of cosmic proportions unfolds!