Abel has long silvery hair, tied up by a black ribbon. He also has blue-gray eyes, and wears small, gray, round glasses with a double bridge. He wears a black priest robe with embroidered crosses and white gloves. He also has two black belts around his hips under the coat. While in Krusnik form, Abel's eyes turn red and a pair of fangs poke between his lips which turn black. He also has a pair of black wings and a red scythe created from his blood: which is stronger than steel and harder than diamond. The wings allow him to fly in the sky and have the ability to generate bio-electric fields.
In the novels, it is mentioned he has silver hair, sometimes blonde-silver, and appears to be thirty years old. He is six feet tall and weighs one hundred forty-three pounds.
In The Throne of Roses arc of the manga, he is depicted as a black-eared "The White Rabbit", as opposed to his white-eared brother. His arcana in Thores' tarot cards is The Fool, a reference to his personality and status as the main character.
Abel appears as a clumsy, silly man, completely unfit for his job. He is capable of becoming very serious, especially when confronted with treacherous situations. He also frequently fakes a smile or brushes off comments that he does not want to answer.
The more that Abel activates his Krusnik nanomachines, the more he seems to drift away from himself, evident in the Krusnik nanomachines talking through him (using first person plural). In the anime he generally appears to have more control than the manga, although he is very detached from his surroundings at 80% capacity. His Krusnik form also portrays an alarming thirst for Methuselah blood and destruction. It is also mentioned that when in Krusnik form at 80% Abel has enough power to completely destroy Rome. Despite the implications of his powers, Abel goes to great lengths to hide this ability from other people, referring to it as "a mark of [his] sins."
He has many quirks throughout the series, such as putting thirteen sugars lumps in his tea, and never has more than a few dollars in his wallet at a time.