The setting is a kingdom reminiscent of medieval Europe.

Since ancient times, this nation has sanctified the concept of being "unique." It is believed that the existence of two identical things invites calamity.

The current King and Queen could not bring themselves to kill their newborn twin princes and kept their existence a top secret.

Only the King, the Queen, the wet nurse, and a few select confidants know of the twins' existence.

In public, there is always only the "Prince" and a "Masked Attendant."