The Anime Lad
Mistarcia is home to humans, gods, and demons, who once cooperated to seal the destructive Bahamut. They divided the key between gods and demons so neither side could release that power alone. Two thousand years of peace follow. Then a human woman steals the gods’ half, demonstrating one obvious weakness in the ancient security plan.
Super Eyepatch Fox
Humans, gods, and demons once united against Bahamut and sealed its power. They split the key in two, giving one half to the gods and the other to demons. Two thousand years afterward, a human woman steals the divine half. The fantasy adventure begins with the old balance disturbed, placing three civilizations around one missing object and one dangerous possibility.
Gigguku
Rage of Bahamut opens with humans, gods, and demons sharing a world because all three once needed to stop the same threat. Their solution was to split the seal’s key so no single side could undo it. Then one woman steals the gods’ half. That is an enormous launch point.
Father's Basement
A sealed world-ending creature is familiar fantasy equipment, and the names arrive before the characters have room to breathe. The key arrangement gives the premise useful structure. Gods and demons each hold one half because neither can be trusted with the whole. When a human woman steals the divine half, the crisis crosses every boundary the old peace was designed to maintain.