In the realm of the elite, wealth and longevity are tied to a "bloodline contract," and the sorceress Siren is the sole master of this contract. The Smith family heir's arrogance and provocation led to the failure of their century-old contract renewal, resulting in an instant backlash and the family's swift demise. At the Brown family's request, Siren reactivated the "Spirit Vein Beacon," revealing her identity as a sorceress and crushing all challengers. To preserve her family's fortune, Brown heir Arthur renounced everything and became Siren's disciple. The two, driving a yellow taxi, embarked on a path to suppress dark magic.