This one in particular was an old one which never took off. I got the basic worldbuilding done and established a setting very similar to the werewolf story in some ways (as in, I mean, directly blatantly ripping off large portions of my own story), but also took it in a distinct way. It could feasibly work as a show or an anime/manga even though I envisioned it as a novel, and that's because of how many characters there are and how there isn't much of a plot, even though there are villains which are systematically dealt with.
I think the main inspiration for this story came from an anime (movie? I think it was a movie, maybe a miniseries, but I don't think it was a full show) on SciFi's AniMonday, revolving around a character named Serge (or would it be Surge?), though I'm not absolutely sure.
Basically, the setting: Earth.
A miracle drug was developed which could seemingly give perfect health to any human being, curing any disease, any infection, and even fixing many natural ailments. The drug underwent rigorous testing to no apparent ill effects, human trials, the whole works, and nothing went wrong, so it was mass-produced.
The drug's basic nature: it would force any infection, be it viral, bacterial, or fungal (and I believe I also included parasites), to work in tandem with the body, creating a symbiotic partnership with the host. The previously-was-infection would spread through the body, allowed to exist, but in exchange for its existence, it would become the primary method of protection against harm, any and all harm.
Except, somewhere down the line, mutations began to happen. The majority of the human population by this point had already been inoculated, and even many domesticated animals had been injected, so there was no warning, no defense, and no way of knowing what caused the sudden change. All that was known, is that a change occurred at some point, and suddenly, these infections began to consume their hosts and merge with them in a new way, becoming new lifeforms.
I had names for them all, but I'm throwing them out to use simpler terms.
Virals, from viruses, dominate the world. They are shapeshifting monstrosities (think like Parasyte; they function identically, though at the time, I had not seen the show), which are able to consume everything they touch and in doing so, strengthen themselves. (Think a bit like Hollows eating souls, from Bleach. Or, more likely, the monsters from the show Tokko, which was one of my favorite anime at the time I created this.)
They can mutate, they can even duplicate, cloning themselves (though few do so, as it weakens the host and they don't like doing that), and they are aggressive. They control the majority of the post-mutation earth, and fight amongst each other as warlords, with the strong eating the weaker. They do have servants, but only those that they know they can kill/control at will.
They usually all act in much the same manner, with a similar personality, off of whatever host strain they were. (For instance, the common cold is a common type of viral, and every viral that is the common cold acts nearly identically, but virals from other viruses act slightly differently.)
They do not necessarily all start as humans. At least one of the strongest warlords in the setting was an animal. A viral's intelligence is largely determined by its strength: the smartest ones are the ones who have absorbed the most.
Bactrals, from bacteria, are a more passive people. They hold far less adaptability and far less aggression, being largely passive, but they're actually much tougher than virals, more resilient, stronger, and most importantly, usually smarter, with their intelligence being raised above what they were as humans. Similarly, they retain some of their human host's personality and retain some skills/knowledge (like knowing math), simply having lost the memories.
However, because they're not as quick to mutate, because they spread slower, because they hold less aggression, because they regenerate at a lesser rate, they are not the dominant force in the world, and many are subservient to viral overlords, doing their bidding and also creating things for the virals, as more of a worker/thinker than fighter.
(Basically, think like real-world: viruses are more numerous, spread faster, and can't be treated easily except by our body's natural defenses, but bacteria are larger and more deadly if untreated. When scaled up to super-size, the more numerous, hard-to-counter viruses win out over the less-numerous, easily-countered bacteria, even though bacteria are plenty deadly.)
Fungals, from fungi, are actually one of the few forces in the world capable of opposing virals. When they band together, they can act as a hive mind, exchanging ideas, knowledge, and information, simply by being in close proximity to one another. They aren't aggressive at all, though they do spread out whenever they get the opportunity.
They are, in a sense, similar to bactrals, in that they are even less adaptable than bactrals are, but they are even more resilient, to the point where they can even somewhat-resist virals. (Viral mutability eventually overcomes defenses, but they exist all the same.) Furthermore, while they're not even as strong as a viral, and their intelligence isn't boosted, the advantage is that they are even closer to human: they retain full memories and knowledge of the human, with only their personality altered, thanks to the influence of the hive.
Parals, from parasites, are basically goa'uld: they exist inside the human, are able to take control of the human, can transfer between humans, retain the memories of their host, have a personality of their own, but are otherwise fully, entirely, human. They can even relinquish control to the human, should they choose to do so. They're completely immune to virals, bactrals, and fungals, but because they're populating human bodies and their competition is superhuman, most parals are subservient to others, usually as covert agents.
Then there's a select human resistance: humans who didn't take the drug. They're hunted down routinely and eaten or forcefully converted (especially by fungals, with some bactrals--virals are more fond of the eat option), but they can fight back. They managed, on their own, to develop an anti-bactral weapon, and through coercion, got some bactrals to refine it, first and most importantly into an anti-viral, but later also an anti-fungal and anti-paral. These weapons (which are separate, mind you) don't always work, and are best used when the entity in question has been restrained, but when successful, the entity will be converted into a human, if they have the mass necessary to take that form. (If not, they die.) And a converted human can never be converted by any force again, being permanently human and permanently immune to the four infections. (But still vulnerable to normal diseases.)
They currently have a non-aggression pact with the fungal nations: "we don't forcefully remove members from your hive, and you don't forcefully convert us into more of you". Similarly, they openly accept parals, because parals are largely harmless.
Of course, some parals and some fungals still hunt humans, and some fungal nations have the stance "if the human isn't a known member of the resistance, then the resistance will never know", just as there are parals (and even some fungals) that are working with humans.
That's the world I built.
The protagonist of the series is a young man who has lost his memories of who he is, but inside of him is a viral. Yet the viral in question is...special. In that it's a viral inside of him. As in, not in control of him, not consuming him. The viral is able to take control, or relinquish control, in the same manner a paral can. The viral also has traits which fit closer to a bactral and a fungal: resilient to attack, communicating with each other (parals don't communicate with their human host directly), less aggression, a desire to spread, strength, and intelligence.
This viral entity within him actively communicates with the protagonist, and therein lies the steal from the werewolf story...especially after he runs into the human resistance.
But in my defense, thanks to my own mind and how it works (the whole David thing), wasn't an all-too-unusual thing, to have a young protagonist, with a voice speaking to him that has a supernatural origin.