It tells a forbidden story between 7 siblings. Will this impossible love be the fate of the Shiunji family?

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.

Yuuta Asamura gets a new stepsister after his father remarries, Saki Ayase, who happens to be the number one beauty of the school year.

Spin-off series from Ranking of Kings (2021) that recount the side stories which took place in-between the main events of the original series.

The people of the kingdom look down on the young Prince Bojji, who can neither hear nor speak. They call him "The Useless Prince" while jeering at his supposed foolishness.