Sara Werec, at the age of eleven, watched her elder brother, Ralph, depart for the interstellar frontlines, located 130 light years away. She made a solemn vow that she would one day reunite with him as a fellow warrior. Five years later, Sara attends the Grapera Space Armed Soldier Academy, where she trains as a Reasoner, learning to pilot an advanced weapons system dubbed a "Strain." Sara's world is flipped upside down when enemy forces suddenly attack the academy. In the heat of battle, she faces off against a Strain that proves too powerful for her. Its pilot then takes off his helmet, revealing himself to be none other than her brother Ralph. He kills all of the other students and destroys the academy before disappearing, leaving Sara to grapple with a shattering sense of confusion and disillusionment. In Soukou no Strain, we watch as Sara reenters training with a new identity. Driven by a determination to confront her brother and uncover the reasons behind his actions, she is resolute in making sense of the chaos that has ensued.