The story takes place at Koryo Academy, a high school where students manifest a personal weapon called a Blaze, which is a physical manifestation of their soul. The protagonist, Tooru Kokonoe (sometimes “Tor”), enrolls in the academy driven by tragedy: his younger sister was killed, and he wants to gain power to protect others and possibly avenge her. On entering, Tooru discovers that his Blaze is not a typical weapon — instead of a sword, lance or gun like many classmates, his Blaze takes the form of a shield, making him an “Irregular”. Koryo Academy uses a system called Duo — every student is paired with a partner (their “Duo”), who they train, live, and fight together with. Tooru is paired with Julie Sigtuna, a silver‑haired girl from Scandinavia and a very capable fighter.