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I think this is a call to the prostitution (vampire host), red light district industry (the host club) and drug addiction (the blood) cycle.
Sachi tried to provide blood out of the host club. The host club receptionist acts as a gatekeeper to ensure their vampires gets blood and stay reliant on the host system. Johan gets protection and easy access to blood thanks to the host club. Sachi's blood supply could be seen as a threat to Johan's dependence to the host club, and that's why she's killed.