Sin Kiske, the forbidden child of a human and a magically crafted biological weapon called a Gear, lives in a world where magic has replaced science, and scars from the Gear rebellion remain. Attending his parents’ taboo-breaking wedding, he encounters a mysterious girl with deep hatred for Gears, and their fateful meeting threatens to upend the world once again.
After the decline of the once robust fields of science and technology, a new energy source known as magic fuels the modern era. Humanity creates forbidden biological weapons: Gears. Those Gears eventually stand against humanity in a rebellion. Although they manage to overcome in the struggle for survival known as the Crusades, humanity’s losses are so great that even after several decades pass, their emotional wounds remain unable to fully heal. Sin Kiske, the child of a human and a Gear, heads to his father Ky and mother Dizzy’s wedding ceremony. Their wedding breaks the ultimate taboo: a union between a human and a Gear. Even with the world at peace, it took many years for such a ceremony to come to fruition. Despite the complex array of emotions surrounding it, the wedding ceremony is met with blessings. When suddenly, a mysterious girl appears… The fated child inheriting Gear blood–and the mysterious girl who despises Gears. Their meeting would shake the world.