When the Crimson Calamity descends, the world is transformed and civilization falls apart. Some step from the light into the shadows, commanding iron steeds and standing before thousands to repel the Apostles' attacks. In his previous life, Chen Qingxu was the Fifth Mechanized Engineer of Dongxia. Framed by others and driven into a desperate situation, he activated the Crimson Conversion Device and perished alongside the Chief Mechanized Engineer. When he awakens, he has been reborn on the day of the Knight Examination. Armed with his previous life's combat experience and alchemical knowledge, he overcomes one challenge after another and meets his future comrades. Among the Twelve Ultimate Iron Cavalry, one has been lost—and that missing knight is the key to rewriting fate. In a calamity-ravaged world overrun by Apostles, find it, rewrite destiny, and protect his comrades.