Jasdevi

Jasdevi (ジャスデビ, Jasudebi?) is one of the Noah Family, and represents the "bonds" of Noah. While Jasdevi is his true name and form, he splits up into two Noah, Jasdero (ジャスデロ, Jasudero?) and David (デビット, Debitto?), and is seen as the two up until his fight with Arystar Krory.

David
The more dominant member of the twins. David looks like a rebellious teenager, but because he stays in his Noah form, he is constantly dark-skinned, wears heavy makeup around his eyes and has the stigmata on his forehead. He wears a muscle shirt, pants, and a leather jacket over it. He is the one that usually starts a fight between the twins.

Jasdero
The more submissive of the twins. Jasdero closely resembles a ragdoll due to his wide eyes and his mouth, which has the appearance of being sewn on the sides. His clothes are of the same style, though his belt is reversed, he does not wear an undershirt, and his jacket does not have sleeves. Instead, he wears thick bandages over his forearms and hands, which resemble casts. In addition, he wears what appears to be an adornment made of ribbons that connects to a lantern ball, much like an angler fish's lure. When Jasdevi split most of it's personality went to Jasdero. Jasdero has a very childish personality and usually indulges in self-stimulatory behaviour, like once when he drew on his own face and usually adds unneccessary giggles to the end of his sentences. Though David retains most of the Bond of Noah.

Jasdevi
To become Jasdevi, Jasdero and David shoot each other in the head, after which their shadows merge together. Jasdevi wears a long red robe with hearts on his shoulders and sports very long, blonde hair, which gives him a feminine appearance. He develops freckles but his stigmata are mostly hidden by his large fringe.

Edo arc
Jasdero and David were first seen talking to the Millennium Earl and being given a mission to hunt some innocence. The twins are completely successful in doing it defeating and killing all who stand in their path. They return to the Earl in Toyko later to report what had done.

Later, Jasdero and David are assigned to track down and kill Cross Marian. They chase him all over Europe but are mostly unsuccessful in finding him. When they finally track him down to an inn, they are redirected by a note from him to go to a bar, where they are ambushed by several creditors demanding payment from them on behalf of Cross Marian. This infuriates them greatly, as not only were they forced to do several menial tasks, they had to pay off the remainder of his debts, which amounted to 100 guinea.

When the Exorcists get to Edo (Tokyo) and face off against the Earl and the Noahs. The twins enter the battle against Baron Arystar Krory III and they are fighting evenly. When the Earl levels the entire place to try to get Lenalee Lee's innocence the twins retreat and are ordered activate their part of the ark.

Noah's Ark arc
They later are ordered to guard their part of the ark, but not before they find out from Road Kamelot that Allen Walker is Cross Marian's student, which infuriates their desire for revenge against him.

In the anime, after the Exorcists leave Yu Kanda behind, the pair decides to waylay them, using several tricks like hiding a bomb in a beer bottle and trapping them under a spiked ceiling. However, their tricks backfire on them and the Exorcists manage to advance without much difficulty. After finally being defeated when Allen cheats in roulette, they direct the Exorcists to meet them in their part of the Ark.

When the Exorcists enter the twins' room they demand that Allen repay them the debts that Cross left to them. After being told the amount, Allen turns 'black' and blows off the debt, stating that it was nothing compared to his current debts. He attacks the twins with Crown Clown, but their abilities, unknown by Allen, give them the upper hand. Soon, the other Exorcists step in to even the balance, and they trap Allen in their green bullet after placing the Deceiving Spectacles on everyone, rendering themselves invisible and creating copies of the key Allen received from Tyki. Krory frees him and blocks all attacks headed toward his friends, after discovering that he can somehow sense the pair even though he cannot see them, and works together with Allen to pin them against the wall while Lavi searches for the real key with his 'Bookman eyes'.

While Allen is looking the other way, Jasdero and David summon "Grudge" to swallow up Allen and Krory while taking Lenalee hostage in the process. This infuriates Allen, who destroys "Grudge" with his Crown Clown and proceeds to attack the twins again, who summon a replica of the Millenium Earl in defense. The replica proves to be as formidable as the real thing, and even though the appear to defeat it several times, the replica cannot be destroyed and Allen and Krory are hopelessly outmatched. Just as the replica is about to defeat the two, Lavi finds the real key, opening the doorway and sucking the replica through the doorway, destroying it. Momentarily distracted, the twins are punched by Allen and Krory respectively, smashing into the bookcase. Krory decides he will fight not anyone else. The twins are infuriated when Krory refers to them as brats and decides not to play around anymore. After singing an eerie song referring to their "Bonds", they shoot each other in the head. The twins combine into Jasdevi and attacks the exorcists. Krory defends his friends by drinking a bottle of Chomsuke's blood and blocking the attack.

Krory asks his friends to leave before they get hurt in their battle. Allen wishes him luck and to catch up later. Krory obliges and starts his fight. Jasdevi uses his power of imagination to battle Krory gaining a small advantage in the early battle. Krory counters by filling his hands with blood in a claw shape. The battle continues with no one gaining the advantage until the akuma blood Krory drank wears off. Krory retreats for a moment to drink a second bottle of the blood. This unfortunately weakens him because his body can not completely break down the Akuma virus. Jasdevi watches the act and wonders what Krory drank.

Krory takes the moment to take the advantage landing several major hits. Krory tells him it was akuma blood he drank. Jasdevi can not fathom why anyone would drink that but manages to regain the advantage. Krory's second akuma blood drink wears off completely and is so weakened that he can barely stand. Jasdevi quickly lands blow after blow on the severely weakened exorcist. Krory knows he must drink the final bottle of akuma blood he was given but he did not want to due to the second weakening him so much. Before Krory gets the bottle Jasdevi kicks him down and drinks the bottle himself complaining on the nasty taste. Jasdevi stands Krory up using his power and seals him in an iron maiden. Jasdevi thinking he won leaves but krory fights back. Jasdevi fights the reborn Krory thinking the exorcist has covered himself in blood. Until he looks at the iron maiden and to his horror Krory is still inside the thing. Jasdevi now realizes that the thing fighting is not Krory but just the blood of the exorcist controlled by innocence and processing the mind of him.

Krory quickly takes the advantage to the point where he injures Jasdevi enough for his Innocence-laced blood to infect Jasdevi, resulting in the word innocence being burned into Jasdevi's arm. The Noah tries fighting back by cutting the exorcist in two but it just does nothing and simply increases the amount of opponents. Krory reclaims the akuma's blood by absorbing it back into himself. Krory end the fight by wrapping himself around the Noah and cutting him again and again. The Noah tries fighting back but can not. Jasdevi eventuality gets Krory off and the bloody form of krory returns to his body. Jasdevi severely weakened by the last attack staggers to the door and sits down on the edge, unable to keep together the two beings that make him together anymore. They split apart, falling through the doorway and are presumed deceased after that.

Jasdero and Devi
Jasdero and David fight using a pair of identical golden guns. These guns, however, are mere toys as stated by Lero. The ammo that the pair use are created with the twins' power of "Materialization", which is when they simultaneously think of what ammo to use. They have so far displayed the following ammo:

Blue Bullet: Freezes anything it hits.

Red Bullet: Combines to form a large fireball, which they name "Blazing Red Planet". Can be used at least twice in rapid succession.

White Bullet: Creates a concussive blast capable of extinguishing a massive fireball instantly.

Green Bullet: Traps anything in a green slimy prison.

Purple Bullet: Covers the eyes of their enemies in a purple goo that is impossible to remove, called the "Deceiving Spectacles" after which, the twins can make their enemies see anything that they want. They have used this ability to make themselves invisible, conceal their attacks and make duplicates of the key Tyki Mikk gave to Allen.

In addition to this ability, Jasdero and David can summon a large mud-like creature which takes the appearance of several human corpses called "Grudge".

Jasdevi
In addition to extraordinary strength and speed, Jasdevi has a number of unique abilities, due to the fact that his powers come from the imagination of Jasdero and Debi. The first of these powers is his hair, which can extend, pierce through humans, and act of it's own accord if cut. Jasdevi also displays the ability to harden his body to augment his defense, named the "strongest body imaginable". In addition, he is able to create and manipulate pentacle-shaped screens that he can use as shields or to trap and crush his enemies. With the same power of "Materialization", Jasdevi can create almost anything, although it takes a little time, seen as when he summons a giant iron maiden to substitute for a coffin when he believes that he defeated Krory.