Red Blue, also known as Reddo Burū, introduces Aoba Suzuki, a cynical and sickly-looking high schooler who has grown comfortable living a life of quiet resentment in the shadows. Labeled "blue" for his gloomy disposition and lack of vitality, his world is turned upside down after a chance encounter with Takumi Akazawa, a popular and explosive MMA prodigy who radiates a "red" passion for combat. This clash of personalities sparks a dormant fire within Aoba, leading him to step foot into the brutal, uncompromising world of Mixed Martial Arts. No longer content to be a background character in his own life, he begins a grueling transformation, trading his isolation for the discipline of the gym and the visceral reality of the ring.

Navigating the transition from an outcast to an athlete forces Aoba to face a daunting array of physical powerhouses and his own crippling self-doubt. The stakes reach a fever pitch when he discovers a major turning point in his training: his detached, over-analytical nature the very thing that made him a social misfit is actually a formidable weapon that allows him to dismantle opponents with surgical precision. This shift in perspective changes everything, turning a quest for spite into a genuine pursuit of excellence. Surrounded by rivals who doubt his resolve, Aoba fixes his gaze on a singular, monumental goal: to rise through the ranks and face Takumi on the national stage. He is determined to prove that even a cold heart can ignite with the ferocity needed to reach the pinnacle of the fighting world.