Happiness tells the story of Makoto Okazaki, who is your run of the mill high-schooler, and a closet pervert. One evening he decides to return a DVD to a friend and ventures out into the night. He suddenly notices a person on a nearby rooftop, who then lunges at him before he is able to comprehend everything, bites into his neck, and proceeds to drink his blood. At this point, Makoto notices that the attacker is a beautiful girl who asks him if he wants to live or die, which then prompted Makoto to immediately say yes, and from there his entire life changes forever.

The striking similarity between these two stories is that it introduces a character that is forced into a position against their own will, and must now face the harsh reality of their gruesome transformation. Makoto and Ken had no idea that their lives would change in an instant, and that they must now adapt to a new environment in order to survive. Both are attacked by a female ghoul and are now forced to consume the meat of humans, which initially made their stomach's curdle with disgust, but now must endure it otherwise they die of starvation. The story transforms into a psychological game of cat and mouse, where they must make the critical decision to kill or let their victims live while uncovering the truth behind why it's all happening.

Parasyte looks at the world of Shinichi Izumi, whose life takes a huge turn for the worse when parasitic aliens invaded his city creating a pandemic. These aliens burrow themselves into the brains of unsuspecting humans, using their body as a shield and can morph into an array of forms to feed on other weaker targets. One of these parasites finds its way into Izumi's body, but is unable to locate his brain in time, and ends up in his right hand instead. The parasite named Migi tells Izumi of the threat that these parasites pose to the world, and so the two must act quickly to put an end to the threat, while relying on each other to stay alive.

You'll be surprised to know that the Parasyte series dates back all the way to 1989, and the more current series we are familiar with is simply an adaptation of the manga. The series ran for 6 years under the Afternoon serialization, with over 60 chapters in the entire story. Izumi and Ken have both been thrown into a world where they never expected themselves to be in, which led to an extreme life changing experience. They both were the victims of an attack which cursed them with a power that took over a part of their body. Now Ken and Izumi have to both rely on tactical measures in order to outsmart their opponents, who too also have extremely intelligent strategies to stay one step ahead of them.

Ajin tells the story of a species of the same title and was part of an ongoing experiment in Africa. Ajin are said to have immortality along with supernatural powers, but unlike any normal human, their behaviors differ. Since its first discovery, more and more Ajin have found their way into the present world, and Kei is one of the characters who encounters one in a very tragic way. After walking home from school with his classmates, Kei is struck and killed instantly by an oncoming truck, but is then revived by a mysterious dark matter. After rising from the dead, the towns people immediately targeted him as an Ajin, and from there the hunt begins.

Kei and Izumi suffer at the hands of another by some tragic event, which leads them into a world they never asked to be a part of. They both have transformed into a completely different being, allowing both protagonists to revive themselves after being fatally wounded. They both must now use these new forms as defense mechanisms to help put an end to the terror that is creating torment in their city, but to also protect their loved ones. Neither characters posed a threat to the world prior to their curse, which was undeserving, but now are both targets by humans because of their accidents.

Ganta finds himself in the midst of struggle as he is framed for a bloody crime at school he didn't commit. His entire classroom is butchered by a mysterious cloaked individual in red, and it's now Ganta who must find out who this enemy is while at the same time, making sure his body stays in one piece. Ganta encounters a mysterious young girl named Shiro, who teams up with him in order to run through the games of death at the prison. He must now use his wits along with strong teamwork to get him out of the situation he's in, but to bring him one step closer to the real culprit behind it all.

Both shows involve a young boy whose life takes a turn for the worst when they're thrown into an unexpected scenario without their consent, and must now come up with ways to survive at all costs. Ken and Ganta have been shunned from society and are targeted as the enemy, and now must try and convince the world around them that there's a greater threat advancing. Both manga demonstrate real life issues in society, where the weak are weeded out from the pack, and the strong continue to dominate and create havoc. The two must now pry their way out and ensure that this sinister organization doesn't manifest into something more threatening.

Variante is a bloody story about revenge, psychological burdens, and overcoming inner demons. After witnessing her family being torn apart by the enemy, Aiko is surprised to find herself atop a laboratory table, with all of her limbs in tact. Things turn gritty however, when she notices the horribly grotesque arm grafted onto her body, she soon realizes that the life she had once lived is now a faded memory. Infused with the DNA of a mysterious monster known as Chimera, the arm behave on the will of its master, leaving Aiko with no control over its actions. Alone and frightened, she must now deal with this curse and overcome what lies ahead.

Ken and Aiko are victims of an incident which they had absolutely no control over. The two must now confront their problems while learning to understand their new abilities. Both are frowned upon by those around them since they're entirely different from the rest of society, and must deal with the psychological burdens that this unfortunate event has plagued their lives with. Their enemies share the very same abilities as they do and so they must come to a decision as to whether they should use their powers for good, or to throw themselves into the fire and suffer the consequences. Their natural instincts turn against them as their bodies try to cope with the new DNA that's been infused within them, and must turn to help at any moment's notice.

The evil Millennium Earl plots to destroy the entire existence of humanity with his creation of Akuma, while Allen must deal with his dark past that still plagues his memory. He comes to learn of his curse and must now practice and master his Innocence, an Anti-Akuma weapon, that destroys the Akuma and releases the soul within them from their prison. After spending a number of years under the guidance of General Cross, Allen signs up with The Black Order in hopes to prevent Earl's evil scheme from flourishing, while using his new weapons to bring peace back to the souls that have been tormented.

Both Allen and Ken started off with a normal life until they both ended up with a curse that would change their lives forever. The two possess an unknown power that can be seen through their eye, and use that ability in order to fend off their enemies. They never asked for their powers since it was forced upon them by another being, which enabled them to perform supernatural attacks at will. Both protagonists must come to terms with their new life, enroll in a powerful organization, and dealing with uncertainty at every corner. What's more resembling is that both of them must fight dark creatures while slowly unlocking the door of truth as to what's transpiring around them.