"Absolute Duo" is a manga series set in a world where individuals possess unique weapons called Blaze, manifestations of their souls. The story centers on Tooru Kokonoe, a student at Koryo Academy, an institution training individuals to become skilled warriors known as "Blazers." Tooru's Blaze takes an unusual form—a shield rather than a conventional weapon, marking him as an outlier among his peers. This anomaly draws both curiosity and skepticism from those around him.

At Koryo Academy, students are paired into duos to enhance their combat abilities through synergy. Tooru is partnered with Julie Sigtuna, a silver-haired girl from Scandinavia who wields dual swords. Despite their contrasting personalities and initial misunderstandings, the two gradually develop a strong bond, both in combat and personally. Their partnership becomes central to navigating the challenges posed by the academy's rigorous training and the threats they face.

The narrative explores the dynamics of teamwork, trust, and personal growth as Tooru and Julie confront various adversaries, including rogue Blazers and shadowy organizations. The academy serves as a microcosm of a larger conflict, with hints of a broader conspiracy involving the origins and purpose of Blaze. Tooru's shield, initially seen as a weakness, becomes a symbol of his protective nature and resilience, while Julie's dual swords reflect her fierce determination and combat prowess.

Supporting characters, such as classmates Miyabi Hotaka and Tachibana, add depth to the story, each contributing unique abilities and perspectives. The series balances action-packed battles with moments of character development, delving into themes of identity, purpose, and the power of human connection. As the plot progresses, Tooru and Julie uncover secrets about their world and their own potential, setting the stage for larger confrontations and revelations. The manga combines elements of action, fantasy, and school life, creating a narrative that intertwines personal struggles with overarching conflicts.