More on the inconspicuous side of things might describe it best. He's 6'4", of average muscularity and slightly overweight. His face features blue eyes, a pointed nose, thin lips and a beard trimmed half-heartedly. Jeans, a black leather jacket and a hoodie for the more rainy days are his best friends. Aside from the cigs, of course. Concept:
Rookie with hard to explain talents, unless
The DuClairs are a family of nobles which can be tracked back deep into medieval France, but much of their fame and money has disappeared over the countless turmoils and societal changes of past centuries. Still they maintain a quite significant fortune and economic influence, but only in Europe. The American branch, dating back to the heyday of steamship-powered migration at the end of the 19th century, has never made much progress past the average in their new environment and isn't paid much attention to by family headquarters.
A record in the family register states that Beaumont DuClair, one of Maël's grand-grand-grand-grand-(...)-fathers, once had a joyful night with a woman later accused to be a witch. While she found a fiery death at the stake he subsequently was regarded as a victim having been seduced. A disproportionate fraction of his children and their children in turn either showed signs of mental illnesses, were physically crippled or generally rather frail and short-lived. What was deemed to be an 'evil curse' acted upon him by said witch seemed to fade away over time though and there is no lack of more strictly scientific explanations in present day.
Maël's situation is an entirely different nut to chew on though. He's the first down the bloodline who both inherited enough of the demonic seed planted by the succubus and whose human nature exhibits enough compatibility not for him to end up like his unfortunate predecessors. It's a component rather diluted given the many centuries that have passed since its origin, but it's there and -- that's the actual problem -- never considered explaining itself towards its owner.
Maël can tap into some demonic prowess, temporarily enhancing attributes such as strength, speed and (maybe most important for an investigator) conventional/magical perception to levels that would otherwise be undue not only for someone of his lifestyle, stature and overall background. However, in this state, he also suffers from a bunch of drawbacks such as an alteration of his skin and eyes that might attract or frighten the public to a disadvantageous degree. He becomes generally more prone to violence with bare hands, teeth and blood in particular and overreacts more easily with a certain disregard of his own well-being. It's not like there would be a simple on/off switch, instead it's more like a ritual during which he pushes himself to the borders of his humanity. It also takes time of forced calmness to get himself back to normal again. Things your character wants to happen (probably wont):
Things you as a writer wants to happen (maybe will):
- Maël joined the group of paranormal investigators because he himself is, partly, paranormal. He hopes to discover more of his own nature and how to control it properly. This simply can't be done in the ordinary public environment.
- Find out if there is any way to predict or even influence what will happen to his own childs, should he ever found a family. Too many of those have died in the past.
- Not get dragged into the abyss by some full-blooded demon or get captured by crazy exorcists who might show interest in him when he is blazing like a star for those who can see it.
- Cry 'Havoc!,' and let slip the personal frenzy! Once more unto the warp core breach!
- A good manhunt, maybe ? Be it him being the hunter or the hunted.
- Some comedy is always good, be it ordinary or of a sarcastic subtype