Soul Society has normally stood apart from the living world, focusing instead on the safeguarding of spirits and the destruction of Hollows. However, a recent influx of evil has given many Shinigami pause. Between a renewed outpouring of Rikti invaders, a devious threat to the time-stream and a huge up swelling of villainous power, souls are pouring into Soul Society too quickly, causing an imbalance between it and the living world.

Determining that the threat to the living world was too great, Shinigami have been sent to Paragon City to stave off the rising tide of evil. The Shinigami and allies that man this outpost are referred to as the Guardians of Soul Society. Forming Mirror Squads reflecting the squads of the 13 Courts, the Guardians have accepted a strange mixture of allies to their midst. Vizard, Quincy, humans and even reformed Arrancar have joined the ranks of the Guardians, all in an effort to save a drowning world.

Each Mirror Squad is lead by a captain appointed specifically for their role in the real world. Each reports directly back to Soul Society and the Captain Commander and are all responsible with running the Shinigami outpost. Some of the 13 Court squads are not represented directly, however. The Captain Commander instructed that no 1st squad would be formed, to remind everyone stationed there that there was only ONE Captain Commander. In addition, the 13th squad does not have a set roster or seated officer (see link).