A Catholic priest who seems to be nothing more than a clumsy, absent-minded fool on the surface. In truth, he is a Crusnik, a vampire of extreme, extraordinary power, and is an ancient being, hundreds of years old. He is a vampire that feeds on the blood of vampires. But despite his strength, he adheres to a principle of pacifism and often refuses to outright kill his opponents, also he has sworn to never kill a human again and adheres to that promise regardless of how hard it gets for him to do so. Abel is shown in flashbacks to have a hatred for humanity, but at some point that changes into his current pacifistic and peaceful outlook on life. He acknowledges having greatly sinned at some point in his life, though it is unclear as to what sin he committed, and much of his current personality is based on retribution for his sins. Abel has at one point referred to his Crusnik form as "a mark of his sins", though it is unknown what he meant by that. He has feelings towards Esther Blanchett, though they are more related to her similarities with a woman from his past. In his human form he fights with a gun that shoots silver bullets. As a Crusnik, is able to transform into various forms based on the amount of nanomachines in his body that he activates. In his higher forms he wields a huge scythe materialized from his own blood. In The Star Of Sorrow II, it is revealed that pre-Armageddon, Nightroad was Commander in the UN Air and Space Force involved in the "Red Mars" project. [...]

The following information may contain spoilers for those who wish to read the manga/novel:
On the surface, Abel appears to be a clumsy, absent-minded Catholic priest who has bad luck with money and is always hungry. In reality, he is a Crusnik, a vampire with extraordinary powers that feed especially on other vampires. Nearly a millennium in age, Abel was created in 2088 A.D. as one of four test tube babies whose bodies were infused with Crusnik nanomachines by the Mars human colonists. Abel once had a hatred for humanity and joined the Methuselah in the war against humans after the Armageddon. During the war between the humans and Methuselah, Abel Nightroad killed seven million humans. Lilith's death during the war caused him to abandon his hatred. He spent 900 years weeping and mourning in Lilith's crypt at the Vatican, until a young Caterina Sforza fled there to escape Methuselah assassins. Abel, realizing that it was his task to continue Lilith's work and defend the humans, saved the young Caterina and chose to live on. He joined the AX at its foundation in May, 3055 A.D.

In penance for his earlier sins, Abel now adheres to a strict principle of pacifism and has taken a vow not to kill unless he absolutely must. Though accepting of his Crusnik form, he will generally only use it as a last resort. After meeting Esther, he is reluctant to use his Crusnik form in a battle for fear of her seeing it, and after she does see it for the first time, Abel is extremely distraught and screams in agony. Later he tells her it is the mark of his sins. Notably, in regards to Esther, in the novels and manga, Abel first reveals his Crusnik form during the Star of Sorrow arc, not long after he meets her, and, in the manga, part of her reasons for joining AX is to find out more about Abel (also in the novels, he is nowhere near as distraught for showing her as in the anime). He seems to be oblivious to Esther's romantic feelings for him, and possibly to his own feelings for her. Asthe seems to have noticed, though, and calls him a dunce for not being bothered by Ion's affections for Esther. While he mostly responds to her with fatherly affection, when he thought she had been killed, he lost control of himself and went into Crusnik form, seeming to delight in killing the Methuselah Radu who he thought had killed Esther. It is Esther that helps him return to normal.

Abel eventually learns that Lilith's killer and his brother, Cain, is still alive and swears to find and kill him, once and for all. After Abel finds and confronts him, Cain defeats Abel and sends him into a near death state. While Esther mourns at Abel's grave, Cardinal Caterina retrieves the nanomachines from Lilith's body and sends Father Tres to take them to Abel in order to revive him. Tres delivers them to Abel's grave, both reviving him and allowing him to achieve 100% Crusnik fusion without the insanity that manifested in Cain. Immediately afterwards, Cain arrives and Abel battles him again, but the fight ends in a draw and Abel must continue his quest to destroy his brother, now joined by Ion Fortuna

In his human form, Abel fights with a gun loaded with silver bullets. With 40% of his Crusnik nanomachines activated, his eyes become red, his lips turn dark blue, his teeth become fangs, and a gigantic red scythe composed of crystallized blood materializes in his hands. At 80% activation, his nails turn into claws, grows black wings and he can generate massive amounts of electricity. He can only achieve this form, or higher, if he has fed on a vampire, otherwise there is a risk the nanomachines will refuse the command and cause him to collapse. At 100% activation, he turns into a humanoid creature with dark skin, black bat-like wings, and blue markings that cover his entire body. He also generates more electricity than his 80% form and a second blade forms on the other end of his blood scythe. While in Crusnik form, the blood of Methuselah is drawn to him and goes directly into his body without using his fangs.
(Source: Wikipedia)