The war between human beings and space monsters has continued. The monsters hold the suburbs of the Solar system, and they are going to intrude into the Earth.
In these days, only the children called “TOPLESS” are fighting against the space monsters with “Buster Machines”. They have special abilities and belong to an organization, “Fraternity”.
One day, a girl from a village deep in snowy mountains came to the city. Her name is Nono, and she has a dream to become a space pilot. She begins to work as a waitress at the restaurant, “Diner”, near space port, but she often makes mistakes.
Then, she meets Lark, who works as an ace pilot of Buster Machine and has outstanding technique.
The history opens its new page at that moment.
She gets excited, and calls Lark, “Onee-sama” (My Elder Sister), and she applies for a space pilot. However, Lark says that only those who have TOPLESS abilities can join them, and doesn’t want to care for her.
Just then, a space monster appears on the ground.