"Brave Witches: The Great Petersburg Strategy" is a spin-off of the "Strike Witches" series, set in an alternate World War II-era world where humanity battles alien entities known as Neuroi. The story centers on the 502nd Joint Fighter Wing, also called the Brave Witches, a group of young women who wield Striker Units—mechanical devices that grant them magical abilities and flight capabilities. These witches are humanity's primary defense against the Neuroi, which have overrun much of Europe.

The narrative unfolds in the city of Petersburg, a key strategic location under threat from a massive Neuroi invasion. The 502nd is dispatched to defend the city and its inhabitants, facing overwhelming odds as the Neuroi deploy advanced tactics and powerful new units. The witches must rely on their teamwork, individual strengths, and the guidance of their commander, Major Aleksandra I. Pokryshkin, to overcome the enemy.

The protagonist, Hikari Karibuchi, is a new recruit from Japan who joins the 502nd. Hikari is inexperienced but determined, driven by a desire to protect others and prove herself. Her journey is marked by personal growth as she learns to trust her comrades and harness her abilities. Other key members of the 502nd include the stoic and skilled pilot Georgette Lemare, the cheerful and resourceful Naoe Kanno, and the disciplined and strategic Eila Ilmatar Juutilainen. Each character brings unique skills and perspectives to the team, contributing to their collective success.

The plot focuses on the witches' efforts to repel the Neuroi assault on Petersburg, with intense aerial battles and strategic maneuvers. The stakes escalate as the Neuroi reveal a new, more dangerous form, forcing the witches to adapt and innovate. The series balances action with moments of camaraderie and character development, highlighting the bonds between the witches and their shared commitment to protecting humanity.

"Brave Witches: The Great Petersburg Strategy" expands the "Strike Witches" universe by exploring a new squadron and their challenges, offering a fresh perspective on the ongoing conflict with the Neuroi. The series maintains a focus on teamwork, resilience, and the human spirit in the face of overwhelming adversity.