Three sisters, Hozuki, Kazuki, and Hazuki, are descendants of Galileo Galilei and have completely different personalities and tastes; they never meet eye-to-eye. One day the girls are suddenly attacked by a mysterious organisation. The organisation was after the Galileo Tesoro which Galileo Galilei was said to have discovered. Still unaware of what was going on, the sisters escape on the airship, Hozuki built, after the sudden attack. But it won't be so easy for these three sisters to help each other out in a pinch when they're constantly at odds with each other. What is the Tesoro, and what is the organisation after? And what about the relationship between the sisters? It's a threesome of cute girls, action, and mystery!