Thousands of years ago, almost the entire land of a long-lost nation was swallowed into the abyss, and a crescent moon-shaped gate emerged from the depths. The gate opened and let out streaks of light, which turned to be creatures from the other realm. For a time, the creatures terrorized the humans until someone discovered something resembling ancient runes in what remained of the nation. Humans soon discovered that there are greater creatures that look like humans and have particular abilities that they can lend to humans in the form of a contract. Because of the gate they came from, these creatures were subsequently called crescents. Meanwhile, the lesser creatures with no humanoid form are referred to as void.

The contract itself demands an exchange of equal value to the power granted, an oath to be kept, and a contract duration after which the crescent will devour the contractee.

As in all legends, a saviour appeared who, after forming contracts with a thousand crescents, was able to force all creatures from other realms into the gate and seal it, returning them to their home. The world is currently unaware of the gate's location. Unbeknownst to everyone, however, a woman was left with the seed of a crescent. This mother later gave birth to the world's first marked child with a special power, ushering in a new era.