Three thousand years ago, the earth was destroyed by "monsters" and most humans were "swallowed". Just when people were desperate, a young man stood up. He was still 16 years old and was not timid at all about the monsters. He led the last remaining humans to challenge the monsters and built a 50-meter-high wall to isolate the monsters and establish peace. Humanity finally no longer faced a desperate situation, but at this time, the young man known as the hero disappeared, and the last person sitting on the throne was the young man's former subordinate and former best friend - Is. Since then, human beings have been living within high walls and are divided into five factions - civilians, Royal Knights, Royal Garrison, Royal Ceremony Corps, and Royal Is.
Today, when the Royal Knights were patrolling, they accidentally discovered a basement and some large covers. Inside were five humans like themselves, five children of seven or eight years old, two girls, and three boys.
The Cavaliers immediately reported to the royal family, who said they would move everything here first because they knew that these were "antiques" from five thousand years ago.