@KuroAnsatsu:
What contract breach. Dead Men Don't Talk. B(
(...More seriously: Murder-for-hire is not a well-regulated profession. There is no Yelp. There is no board certification. I don't know about Japan, but in 'muirica the FBI seems to like to pose as hitmen to nab convictions, and it works for them (sometimes this turns awkwardly into entrapment, but that's another story)—a whimsically backstabbing manic psychopath like this protagonist could certainly also continue to find jobs.
Though I'd be careful if my client was the yakuza, admittedly.)