At first I thought this manga was a plagiarism of Parasite with a few drops of Gantz, My Hero Academia, and a little bit of mahou shoujo (talking animal partners). Albeit this is indeed the case, the story has its merits. It is a reflection on the conflict between a person’s real motivations, intentions and wishes and the overwhelming stress that is living in modern Japanese society, all the roles and impositions you have to fit to be considered a good citizen. The society is sick and the symptoms are high suicide rates, nervous breakdowns (my case in particular despite I am not Japanese), the hikikomori people, and so on.
The intensity of the internal conflict between a person’s desires and self satisfaction versus the chains and roles imposed by society, the mediocrity of life, and the ultimate impossibility of ever attain happiness is the trigger that makes one a victim to the monster infection, therefore becoming a monster driven by its own frustration and killing rage. The (dark) hero being one of these.
Unusually there is a gender bender subplot that adds a special flavor to what otherwise would be our average story of monster hunting, gore filled, killing spree. It shows that to the women the impositions of the society are different and even harder to meet than that is to the men. Also how more vulnerable they are to violence — sexual violence mainly— than the average man. How the care and time they need to devote to their appearance and body is much bigger and how they experience sex intercourse is also different. I came to like Airi more than any other character.
Other satisfactory ingredients are romance and sex— lots of sex. This really surprised me, heroes in this genre of stories don’t experience sexual desire, it is a sin if the hero stains himself (or herself) with the lowly needs of the flesh. However this manga is exactly about desires and the impossibility to ever reach satisfaction in one’s life, thus leaving sex aside would be inconsistent. And, come on, people like sex a little bit more than violence and killing.
To my pleasure the ending is good, because very often even good manga and anime have lousy endings that let us down. The bad side of this manga is the art. We clearly see that there is a contrast between the background and scenery in general and the character design. At some point it seems that there are two different people drawing. While the scenery is mostly well drawn up to the end, the character design more and more degrades almost to comic book levels in the final three or four volumes. All the women have the same face, the faces become distorted as well as the bodies. Every character becomes generic and low quality, art wise, to the point it was painful to my eyes reading the final volumes. After all they had to screw up somewhere in what otherwise would be an enjoyable reading.
P.S.: Why the hell the scanlators transliterate ジャガーン as “Jagaaaaaan”? The right way would be “Jagaan” with two “a” only.