I have a different approach to my character it seems. I made a background that does have some detail in it, but otherwise is very open. Partly because at the time I didn't have same some vamp facts and found it best to leave some wiggle room. And because I really didn't want to think it out too much. Leaving it open, gives me room to work things in as I move along.
So this is not really about the background of my character, but more about the character concept.
Tetsuo/the narrative often refers to his vampire side as a demon or monster. I got the idea from a book series I read. Those two books tell a fantasy version of the Beast of Gévaudan story, which is a story about werewolfs (and beasts of various other animal races).
The were-creatures in this story can change their form at will at any time, but are forced to change at the three days of fullmoon. They really have a beast inside them. A different being with it's own conscious. After around a year the human part side is completely gone. Although there are some that don't kill humans and are not evil.
The story takes place in two story lines that change back and forth. One is set in the 18th century at the time of the original murders where the story begins, and the the other is set around the time it ends. The protagonist of the present storyline is an ancestor of the guy that starts it all, and is hunting were-creatures like every other family member before him. Only that he is a werewolf too, born with the demon inside him.
It hasn't however taken him over. He uses drops of gamma-Hydroxybutyric acid to dull the beast enough to be able to hold it with his mind, and has done it for years.
But the beasts haunts him with terrible pictures of times he has failed or made up stuff, and speaks to him (Think I'm gonna do that in the future. but more straight forward than the wacky doctor's voice).
I used that part about him for my character. The training to deal with the urges. A way to keep a hold over the beast, even if in another way, and strenghten it over time. My character has actually trained to prolong the time between meals over time. That combined with the fact that he let's it loose from time to time, strenghten his hold over his urges.
The other thing I used is the fact that it's like a different being. A dark passenger if you will. I realize that a werewolf and a "vampire" made by nanomachines are two different things, but I look at it this way.
I'm not saying vampires have a beast inside them, just that Tetsuo is seeing it that way.
Talking about the dark passenger. You could say Tetsuo's code of killing criminals comes from Dexter. I hadn't however seen the show when I came up with the character.
"For Feanor was made the mightiest in all parts of body and mind, in valour, in endurance, in beauty, in understanding, in skill, in strength and subtlety alike, of all the Children of Illuvatar, and a bright flame was in him"