Comment on Creating a Well-Developed Original Character by amber-sky

Not sure if you're even going to see this, but here goes.

I have a character in a similar situation for a fanfiction of an anime called Yu Yu Hakusho.  Her name is Hotaru Kuwabara, and she is the sister of one of the main protagonists.  Her backstory is kinda long, and goes into her previous incarnations and whatnot, so I'll just stick with the basics.  She has two souls, essentially.  One is the human soul, which is the center of emotion and morality.  The other is the Fae soul, which was passed on through her family and was the soul of an ancestor.  The soul is essentially a mas of sentient energy, and its presence affects her personality, making her a little more socially inept and unable to feel things quite as much as others.

She endures a traumatic event, which allows the fae soul, or fae energy, to be unleashed.  It protects her, but is too powerful and is killing her in the process.  Having used that energy for the first time, it all but eliminated contact between her brain and her human soul, resulting in sociopathic tendencies.  The fae soul existing initially allowed for 50%contact between her brain and soul, but after she used it, it became more prominent, and blocked off all but 12% of her soul, resulting in a loss of emotions.

Considering your character is able to share his body with spirits, it would make sense for their personalities to mesh with his depending on what they are like.  He doesn't necessarily have to be a sociopath, but he could have a very mellow, apathetic personality.  Or, the fact that he lost half his soul could mean he lost half of his emotional strength thus leaving him a sociopath, meaning his soul is constantly searching for completion, hence why he is able to connect with spirits.  It would be interesting to see the character change depending on the personality of the spirit he merges with.  This is a really neat idea you have!

For backstory purposes, you need to first decide on what your character is like now, then look at examples of similar people in reality.  Find out what made them the way they are, and go from there.  If you still plan on him losing half of his soul (if you don't mind, I might use this myself, but I'll credit you with the idea), then figure out how and why he would have lost it.  Where was he when it happened?  Who did it?  Why did they do it?  Why was he there?  Who does he normally associate with or what does he normally do that might land him in that situation?  Why did he maybe go outside the norm and go somewhere different?