Asuhara Gin is a highly promising young detective with exceptional physical abilities. However, after a certain incident, he forms a subordinate-master contract with veteran detective Mera Shūsui. Together, as an unlikely and twisted detective duo, they hunt down brutal criminals—including cooperating in “collecting the blood of criminals” as part of their pact. Their main target becomes “Z,” a horrific serial killer. The contract and their pursuit thrust Gin into the dark depths of the criminal world, challenging both his morals and his survival. Gin must balance the demands of his new master, the dangerous pact, and the horrors of a relentless investigation.

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