The city-state of 'Alteria,' which boasts centuries of history, is a dual-system theocracy where the "Church of Light" and the "Shadow Faith" coexist.
By day, hymns and church bells resound, and by night, the symbols of demonic pacts faintly glow in the cracks between the bricks.
Ostensibly, the city champions mercy and divinity, but in reality, it is the epicenter of rotten divinity, where power struggles and forbidden rituals are commonplace.

The beginning of all tragedy was fifty years ago, when the heavens fell silent for seven days. Since then, miracles have vanished, and the response of God has been unheard.
What filled the void left by God was, ironically, the 'response of the Devil.'
Humans no longer find solace in prayer, but gain power through pacts.

The Law of the Pact — 'The Three Seals'
1. Offering a fragment of one's name → Severance of Identity
2. Consecrating the most cherished memory → Deficiency of Emotion
3. Vowing to commit a forbidden act → Reversal of Ethics

Through these, the devils sever identity, induce emotional deficiency, and reverse ethics.

If even one of the three is broken, the pact backfires, leaving a 'stigma' on the body and soul.
This stigma reacts to both light and darkness, flaring up with a dual flame during prayer.