To love a caterpillar

[Brandnewbuddy]

So more of a theme than an idea (though I’ll toss out one or two): a lover or a friend is undergoing a transformation that they feel will improve them. Whether literal or metaphorical doesn’t matter, but as that person reaches a point of no return, the main character can’t help but think of how much they prefer the person they are or used to be before the transformation.

This would be a darker theme obviously. I had thought of a nonerotic application but it was a from a different POV.

A couple ideas:

1. Fantasy or sci-fi: a person is dating a being that undergoes a metamorphosis. They start as a somewhat average looking human but they then change into an awe inspiring beautiful creature that literally soars above everyone. Lover is very excited and is eager with the prep work but MC…well they are less thrilled. If their partner undergoes that transformation, why would they stay with MC…and it gets them to thinking of some dark thoughts. Maybe they try to stop the transformation, maybe they let it happen but gather up the cocoon and animate it into their partner’s former form.

2. Partner in this case is getting clean. MC was always there when they were coming down, made sure they had a safe place to crash, and was always there for rebound sex. However, as partner is getting clean, they spend less time with MC and even start accusing MC of enabling them…which isn’t an outright lie but there’s a ring of truth to it. MC should want them to get clean but…would it be so bad if they had one or two little relapses to remind them how tender passionate MC can be when they hit rock bottom.

 

[Husky_Embrace]

As we're still seemingly brainstorming, I had an idea that is similar enough that it might he adapted, though it focused more on the part before the transformation.

Some sort of symbiote/parasite (not like the movie) that has a chance to infect people. If infected, people are unable to do something after a certain stage. The symbiote is certainly to take root.

It is a symbiote in the sense that it doesn't kill or is bad for the person as a whole in the long run. It could improve them over time. However, it is seen as a parasite as it'll take over the brain over time. It'll change the personality that the 'original' person is seen as dead, and the parasite lives with all learned skills and memories.

A person is diagnosed with the symbiote/parasite. You follow their partners life as they come to terms with it. The changes the symbiote/parasite introduces maybe changing some other things as well. Eventually the person is taken over. Maybe they still try after the change.

My vote would be Cordysceps, a fungal growth where a few subspecies can take over a host of other creatures, mostly insects. The one taking over humans improves the human, allowing the body to survive longer and thus increasing the chances it can spread, which is likely to be low on such complex creatures as humans.

If you want to stay at least somewhat realistic, the fungus can operate with the assumption that there's more than enough food, removing many restrictions a normal human has. They eat a lot, but use it too. Muscles easily grow, the brain is overactive, making them more tireless, motivated and able to concentrate, etc.

You could argue that after a certain amount of time the body starts to feel ill effects, like burn out and such. For one it takes a year, another 30. The fungal doesn't care and eventually depletes the body, as it has had all that time to spread.

TL: DR
Symbiotic entity infects human. They start growing into a superhuman that eats a lot, are generally stronger and motivated, until after a year or decade they decline. The symbiotic entity takes over the human after a certain amount of time, making their personality before and after different.