Omen is what happens when the universe divides by zero: it happens every now and then, an edge case involving the RNG in the sky causing someone to be born with zero luck, resulting in a math exception error and creating a deep gravity well for fortune.
Now, everywhere they go, Omen constantly and passively swallows the luck of others. This isn't luck in the broad sense we understand it: their power works on the level of discrete information and can shape physical events, but not necessarily decisions. They don't enjoy an increase in luck themself, either, but oftentimes just the ability to make an opponent unluckier than oneself is extremely useful on its own.
After sucking a few casinos completely dry, they are now banned from entering at least 50 gambling establishments in five different cities, and everyone knows better than to play against them. Other places from which they are banned include hospitals, disaster zones and areas of high risk. In a bizarre self-fulfilling prophecy, they've become a bad omen in their own right.
The strength of their luck-guzzling capabilities can change with the wind; on some days, they get to keep more of the luck they steal than on others. They carry six golden dice in the case hanging around their neck, rolling them to determine the current levels.
Of course, the greater the degree of one's undeserved fortune, the stronger one attracts the harbingers of death and justice. Omen knows someone of an otherworldly nature is chasing them, and they've had to start making plans.