On a planet called Era, people are bound to one of the Seven Deadly Sins before their first birthday via a religious ceremony called the Nexus Ritual. All their life, the inhabitants of Era have to fight against their urges. Should they fail and succumb, they transform into mindless and aggressive beasts. The Unio religion representatives – the Arkhons – ensure that everyone follows the rules and put down any monsters that appear in the cities.

One day, a woman gives birth to twins, something that never happened before. The Prime Arkhon, supreme leader of Era, conducts the Nexus Ritual himself. However, something goes wrong, and one baby is bound to all seven sins, while the other receives none.

The twins are taken to the capital, Avilah, where they are brought up as Arkhon apprentices. They are never allowed to leave the walls of the sanctuary…
But one day, Leht, the twin bound to the seven sins, manages to leave the city. His brother Cyphel is sent on a mission to find and bring him back. He is accompanied by two seasoned Arkhons, Gram and Enki.

The journey of Cyphel and Leht is one of self-discovery, one that will allow them to grow and become the people they were destined to be.