Hiraga Raizou has just entered retirement from the Japan Metropolitan Police Department (MPD). But hearing his grandson is afflicted with a rare disease costing a million yen a month in treatments, he resolved to raise the necessary money for his grandson's sake. Seeing a job ad seemingly tailored to his skillset brings him to the 'Desperado' used books store, and he is sent for a trial work... as Cleanup Crew for the assassin employed by the organization, the little girl Suzukaze Miharu.
- Badass and Child Duo: Played with in that Hiraga himself is a badass, but it's the kid Miharu who pulls the trigger most of the time.
- Big Bad: Musou Saburou, the leader behind The Greatest Bond. Overlaps with Diabolical Mastermind.
- Nebulous Criminal Conspiracy: Known as 'The Greatest Bond' in the underworld, it comprises Dirty Cops, Corrupt Corporate Executives, Corrupt Politicians and more within its ranks.
- Dissonant Serenity: Director Kinume's expression barely changes from 'disinterested look'. Not even when she approves the hit on her own biological father.
- Enfante Terrible: Miharu is Desperado's primary hitman. At one point her would-be-victim called her a 'murderous demon-child', and her response is for him to keep talking as it 'makes her tingle'.
- Healthcare Motivation: Raizou takes the job to earn money for his grandson's medical treatment.
- Murder, Inc.: The Desperado used books store is a front for the SS Agency, a government-sanctioned (or so they claimed) extralegal entity seeking to bring 'justice' to those who would otherwise evade it.
- Retired Badass: Raizou is a retired officer whose training comes in handy for his new career.
- Reused Character Design: Hiraga is basically Dr. Coppelius minus the cracked glasses.
- Revenge: Miharu's prime motivation of becoming a hitman. Her father knew too much and The Greatest Bond eliminated him and his family. Miharu missed the hit and swore vengeance to all of them.