Synopsis

In the distant future, mankind is divided into two powers; Union and Deague. They have continued a war so long that no one is sure when it began. Union uses manned weapons, Strain is the main military power, while Deague uses unmanned weapons Tumoru.

Sara Viereck, a daughter of a good family, is a Union?s 16-year-old girl who goes to Grapera Space Armed Soldier Academy located in Cranial Solar System in order to become a full-fledged Reasoner (a pilot of Strain).

Her brother, Ralph Viereck, was sent to the front line 130 light years away to accomplish a special mission when she was 11 years old. It takes 400 years of objective time even by the fastest sub-light speed space craft of Union to travel that distance. However, according to relativistic theory, it corresponds to two subjective years (the time crews experiences). Therefore, Sara needs to go to the same battle field to meet her brother.

Because they lost their parents when they were quite young, Sara thinks of her bother as a guy dearer than a sibling, and she lives for their reunion.

One day, the planet Sara lives is suddenly assaulted by Deague. Surprisingly, it was her brother Ralph that takes away a mysterious girl sleeping in a capsule.

To search for the truth, Sara gets in Strain and runs after him. However, she receives an attack from Ralph, and the Mimic is broken. The Mimic is a copy of the pilot?s brain, and it is an essential part to control the Strain.