A sentient race of neural parasites is in a civil war between the Symbiotes, who've used their extensive knowledge of genetic engineering to alter themselves into symbiotes, and the Parasites who think the Symbiotes have made a mockery of their way of life and seek to wipe them out. The Parasites outnumber the Symbiotes massively and have driven them into hiding.
- Both the parasites and the symbiotes are small, squid-like beings similar in size to the larval stage of D&D Illithids, that can infect any species that has a brain roughly similar in size and shape to a human brain. They burrow into the host's neck and then alter the host's DNA, RNA, and body, resulting in radical internal changes. Externally, the only difference is a small lump on the back of the neck. Basically, they're the weird lovechild of a Goa'uld from Stargate and a D&D Illithid.
- How the control works depends on whether we're dealing with a Symbiote or Parasites. Parasites take over the host's Nervous system, trapping the host in their own body. Symbiotes, on the other hand, have control at the same time the Host does, allowing for multitasking. Conflicting commands cause the body to simply listen to neither command until the issue is resolved. The Symbiont also intimately shares thoughts, feelings, and memories with the host and vice versa, which means that conflicts are rare, and happen at the speed of thought when they do.
- Some of them grant abilities that both the host and the Symbiont have access to (or just the Parasite, in the case of them), such as gravity manipulation and electromagnetic field manipulation. Don't even ask how they do this, they don't know either, though psionic capabilities may or may not be involved.
- This is not reversible. The symbiont/parasite can abandon the host, but to do so they must do extensive damage to the nervous system and brain in the process, killing them at best and leaving them with massive brain damage at worst. There are surgical procedures that can separate the symbiont without killing the host, but these are incredibly challenging even for the aliens, and still leave the host with brain damage.
- Due to the relative irreversibility of a bond, informed consent where the host knows what they're getting into by agreeing to this and agrees without being coerced or on a whim is essential. This presents a slight problem for the Symbiotes undercover among the Parasites, as the Parasites don't give a damn about what the host wants.
- The symbiotes and parasites hail from an earth-like world, and thus, due to convergent evolution, they have psychology and thought-processes similar to our own, and feel the same emotions. As you can probably tell, this means the divide between them is reflective of modern political divides between Americans: the parasites would lean conservative, while the Symbiotes would lean liberal.
Let's say a symbiote must take a host whilst undercover in Parasite territory. Unfortunately, the host didn't want to host anything, Symbiote or Parasite, in the first place, but the Symbiote had to take the host anyway or risk blowing its cover.
What might be the short-term and long-term psychological consequences, both for the host and the Symbiont, for having to integrate with a host that didn't agree to this?