Rocopon

As far as the public is concerned, Rocopon—earth's only alien—hasn't done much but loaf around in the 8 years since he crash-landed in Tokyo with no memory of his past. Granted, that is what he likes to do, and he does spend a lot of time playing video games. But as an alien to whom earth laws technically do not apply, he's been hard at work in a top-secret capacity: government-sanctioned extrajudicial assassin, cleaning up the worst of society that the law is either too slow or too powerless to confront. After years of dispatching hapless crime lords and their goons, things have gotten comfortable. But Rocopon is about to meet his match in more ways than one—fed up with his sloppy ways, headquarters has assigned him a straight-laced partner, and the criminal underground has enlisted the help of those who are a little more than human... (Source: Kodansha USA)