Silencer(2012)

Silencer

Shizuka is a policewoman who loves her silencer more than anything. Back in Japan after an internship in the United States, she is banned from the police. Transferred to the sordid "Security Annex Office," she has to team up with a corrupt and perverse coworker. During a trivial investigation, she witnesses an atrocious murder and decides to lead the investigation. She does not know it yet, but she's going to encounter a terrible threat!

(Source: Nautiljon, translated)