Demitri wears a black and red organic-looking bodysuit, he wears a silver helmet covered with dark glass, hiding his face from view. It's that he has a similar face to the Noah, although he possesses similar golden-yellow eyes and black hair he however has instead pale skin. His "Guilt" is known the Gears of Fate, powerful in their design and able to channel Dark energy as well as Elemental Attacks down their length.
Demitri has been seen to be kind and spare certain people he knows, he is also at times valiant, values friendship, and possesses heroic qualities. However all these positive attributes go out the window when he becomes "as a being created from the purest of darkness", despite their being present when around Sorath, possibly due to his feelings for Sorath.
Demitri is proud, cunning, cruel, and described as pure evil. The lives of others, including that of even his Allies, hold absolutely no value to him, he shows no remorse for his actions, and as a pragmatist, he will strike without a moment's thought or warning, seen when he strikes at Lavi when in an ambush and attempts to eliminate him. He has disregarded his master's orders on occasion despite his loyalty to Sorath, an event demonstrating this being his attempt to destroy Allen in their first battle, despite the fact that doing this would interfere with Sorath's plans. He is also shown to be uncaring, having no sympathy for anyone but himself and Sorath.
He can also be overconfident at times. He also seems to enjoy fighting, an event demonstrating this being after Lenalee defeated him in their first battle and tried to remove his helmet, he bursts into a fit of hysterical laughter. Though he can comprehend mercy, he rarely gives it, usually being either in an excellent mood or seeing some kind of unknown importance in the opponent.