By now I suppose most of us are familiar with how something delivered with the trappings of one genre turns out to be a resident of another. A-Jin (or "Demi-Human", as it's been subtitled in English) takes the cast of a shōnen story, drops it headfirst into a seinen work, and lets the audience cross its fingers and pray that our heroes will land on their feet, or at the very least break nothing vital. A-Jin also sports one devilishly clever premise to ensnare those heroes in, and also hints that said premise is merely the starting point for a far larger, more complex set of explorations.
First, the premise. Walking among us are a subclass of humans, the a-jin or demi-humans of the title. They are indistinguishable from other humans save for one massive difference: they don't die. Put a bullet through their heads, rip them in half, squash them under a truck's wheels, and they reconstitute. They're not immune to pain, however, so the deal is not nearly as good as it might seem — especially if the authorities find out you're one, kidnap you, and subject you to an endless regimen of experiments (read: torture).
Kei, a kid in high school, has no idea that he's a demi-human until the day he mistakenly steps in front of a truck and gets back up again. Most every other demi-human out there is at the same disadvantage: they don't know they are one until it's too late. Once Kei finds out — that is, once he drags his bloodied self out from under the truck that road-killed him — his first impulse is to do what any sane, rational person would do: run like hell. He buddies up with his sorta-kinda friend Kaito, who is as outwardly thuggish and punkish as Kei is straightlaced and goody-goody, and the two of them go on the high-speed lam from the agents of a secretive agency tasked with finding the demi-humans.
What I have just described is the bare outlines of the plot, which provides the words but not the music for this story. How all this plays out — the specific details, the energy, the vigor in the artwork — puts A-Jin way above the average. It also has the wisdom to give us a main character who is no less canny than anyone else in the audience, meaning it's a pleasure to watch him staying one step ahead of his captors. He learns at least as fast as we do.
If there is a flaw in the story construction, it's in how this mix of plot advancement and character development sometimes seems forced. At one point Kei logic-chops his way to the conclusion that if there are others like him, they must have their own secret society, and will therefore let him in too. This element in particular feels less like Kei being smart and more like the writers trying to both demonstrate that and front-load information about the setting, with both coming off as heavy-handed. But on the whole, the speed, the inventiveness, and the promise the story holds are all reason enough to read it. This will be one to stick around for.