He's a good guy, but he's not professional. I mean, he was binded by the contract yet he's breaching it by betraying his client.
No one would ever trust and hire him lol.
I called it last chapter. This guy's way too much of a softie for this job. Then again... this soft side may well be restricted to his preference for fluffy romances with how he was gonna shoot her too until the guy tried shielding her.
(...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.)