Hey everyone.  I've been getting back into the swing of writing these last few weeks (and I appreciate all of you who've enjoyed my writing so far).  That said, I've always wanted to do a long work, but have never been able to commit to one.

I bring this up because there's a project, or at least an outline for one, in my head that I want to do.  I feel a little like this project is special because variations of it have consistently been in my head for years, even though they are constantly changing and varied.  The consistent part is this:

A group of energy-based lifeforms continuously reincarnate.  They do this by merging with the soul of an unborn sentient creature after their last host dies.  They lay dormant until the child reaches maturity, at which point the child begins to gain memories of past lives, and manifesting powers based on the type of creature (there are several different "species," and a few that are special cases and have powers no one else has).  Eventually, the two identities are fully merged.  This creates an underlying philosophical question: was the child consumed by a parasite, or was the child granted immortality by merging and becoming part of something greater.

The characters and basic plotlines of these setups have varied wildly.  Oftentimes I've had the idea that these creatures are interplanetary, and Earth is considered an unimportant, outlier planet, with only a relatively few, weaker parasites (for lack of a better word) on it, and suddenly an incredibly powerful, incredibly dangerous parasite is reborn there, who could have easily been handled on a more central world, but is almost unstoppable here.

More recently, though, I've been thinking of confining the story entirely to Earth.

I've also debated if there are circumstances under which they could fail to fully merge with their hosts, or be permanently killed.

I don't know, what do you guys think of this idea, and where would you go with it?