Gin Tama, Vol. 1 by Hideaki Sorachi

[Viz] It's samurai vs. aliens! The samurai didn't stand a chance. First, the aliens invaded Japan. Next, they took all the jobs. And then they confiscated everyone's swords. So what does a hotheaded former samurai like Gintoki "Gin" Sakata do to make ends meet? Take any odd job that comes his way, even if it means losing his dignity. Nobody with Naturally Wavy Hair Can Be That Bad Sleazy alien moneylenders, monsters on the rampage, and a ticking time bomb may all be in a day's work for Gin, but a drop in his blood sugar level means trouble for everyone!