I watched the Ajin anime when it aired, and I loved it despite the weird graphics. It was a great concept, with a very nice execution. Its characters were awesome, and I was looking forward to reading the manga once it would be finished.
Sadly, it didn't live up to my expectations...
Ajins are immortal beings. They revive as soon as they die. Of course, such a phenomenon would be the target of governments around the world. They capture known Ajins, and experiment on them.
One day, Kei gets run over by a truck. But he doesn't die. Everyone now knows he's an Ajin. He has to run away to keep his freedom. He'll be quickly contacted by Sato, another Japanese Ajin who plans to make drastic changes in the History of Ajins.
This is all great. This manga is packed with a lot of story revolving Ajins, while displaying great action scenes. The way it uses the Ajin power was brillant.
It has a nice balance between plot and action... up until the second half of the manga.
Basically, Sato's plan consists of three waves of terrorism. While the first two waves are intelligent and well balanced, the third one lasts too long and is way too straightforward. There isn't any twist, there isn't any plot-evolving event. That final battle is just a bunch of fights and explosions. It's spectacular... but way too long. And the plot suffers from that.
It doesn't help that everything is thrown out. The final confrontation consists of a single stare on a bridge... People leave the story at random times (through death or not), and all those endings feel like they were thrown just because the author got sick of writing it.
I just don't feel like this ending was really conclusive. The entire manga is great, but only feels like a beginning rushed into an ending because the author got bored of what he wrote. Frankly, I prefer the end of the anime.
I really like the drawings. It's rare that action scenes work in a manga, but in this one, it works brillantly.
This is the strong point of Ajin. Kei's morality is genius: as a rational person, he keeps pretending he doesn't care about anyone, but he actually does. That results in conflicts between his dialogues and his true thoughts. This was brillantly used, and a perfect example on how to play with a character's morality.
Sato, of course, is the best character in this story. He's charismatic, he's intelligent, he's badass, he's insane, and he has a nice story. The way he views the real world as a videogame was brillant: for an Ajin, who revives after he dies, real life really is just game.
The two mains are awesome, but the support cast is great too!
I love Kai, he's the best of best friends. It's a shame his role never get really big... I also loved Kei's family. They're not very important to the plot, but their few scenes are interesting.
Tosaki and his assistant were a nice combination. Somehow I feel like their complicity was better in the anime.
And of course, there's Tanaka. That one is awesome too! In my opinion, he carries this series on his shoulders for a while. His inner conflict was a nice story to follow, and his relationship with other characters were interesting.
The final arc utterly ruins this manga imo. But Ajin is still a very interesting story! I recommend watching the anime, you won't be left on an unsatisfying note. If you really want more after that, then you carn read it, there's a few interesting cut content.