Parasyte

Definitely one of the wierdest shows I've ever seen, Parasyte is a rather complicated story about a young man who's hand is taken over by...well, we don't exactly know what, but for lack of a better term, it's a parasite. And it's not alone, there are more, and they don't like the boy who's parasite isn't attached right, forcing the two to fight for survival.

So they don't explain the biology very well, and I feel I need to explain what I've been able to deduce. The parasites begin by hatching out of spores in a larval form which seems to seek out nervous tissue to consume, the richest and most desirable source being the human brain. Once they find a source of nervous tissue, they consume it and in the process go through a metamorphosis, resulting in the parasite merging with the surrounding tissue into a mature form that can continue to transform with few limits, one of the most significant being that their mass is fixed, another being that they don't acually take over the whole body, just a part of it. The drawback of their shapeshifting abilities is that since they have no stable body, they can not support themselves and must rmain attachedto a fixed body with the right organs. Ideally, the parasites take over the head which by proxy allows control over the central nervous system and therefore the entire body, but they only shapeshift the head and are limited to the mass of that body part regardless of what shape they take, defaulting to whatever that part of the body looked like before they took over. Most cases are the ideal situation of taking the head, but there are a few oddballs that tell us about the other limitations; they can switch hosts if necessary, but not species or genders, the new host must be of the same species and gender as the one they matured with(most likely due to hormones and DNA like an organ match), and if they take over a part other than the head, the lack of nervous tissue will prevent the mature parasite from being able to control a full body and will always be limited to other body parts. The parasites draw unwanted attention when they kill humans, operating under simple instincts to continue eating human brains, it takes a while before they realize they can eat normal foods and when it nourishes their body it will in turn nourish the parasite, but they already have the police on them before they figure this out. Another quirk is that they can sense each other, though this seems to actually cause more trouble than it prevents.

The main case in this story is Shinichi and Migi. Migi tried to go after Shinichi's brain through his ear, which usually works fine, except that Shinichi fell asleep weaing headphones which prevents Migi from entering so Migi tries his nose which causes him to sneeze, expelling Migi and waking up. Migi desperately tries to go after Shinichi again, but Shinichi blocks with hi right hand and desperately uses his head phone wire as a tourniquet to prevent the worm from crawling up his arm into his body. By cutting off his circulation, Shinichi forces Migi to settle for being just his right arm. Migi is able to adapt to the less than ideal situation easily enough, but other parasites can sense migi and once it becomes clear he's not the head, they assume he's a failure and they must eliminate the pair. It also doesn't help that Shinichi feels responsible for protecting the innocents around him forcing Migi to fight to keep both of them alive. Migi isn't compelled to eat human brains, being sustained sufficiently by Shinichi's bloodstream, but his dependence on Shinichi for his own survival makes him do things for Shinichi that he'd rather not do just to keep his own support system going. The story becomes more complex as the conflict between the parasites and the humans grow more personal for Shinichi and Migi, they come for Shinichi's mother and his girlfriend, and after studying how the duo functions, they start makign their own Frankenstein monster of multiple parasites to one body.

I can't say much more without giving away bg spoilers, so if you're interested, tune into Toonami at 1AM EST.