Born nameless to a woman who worked in a brothel (died after childbirth), the mistress of the establishment took the babe with the disfigured arm to an orphanage. The workers there named him Allen and his shrivelled arm was amputated, a tech-prosthetic that would grow with him put in its place. Allen ran away from the orphanage at the age of seven, becoming one of the many street rats in the city. Until one day he was picked up by a street performer named Mana after he had been beaten for having been caught stealing bread.
Mana took care of him with his meager funds and offered a proposition to Allen: go back to the streets or stay with him and learn a living in acrobatics. The man's kindness had struck a cord in Allen and he decided to stay with Mana until the older man was brutally murdered for his earnings of the day when Allen was stuck home sick. It took all of Mana's savings - what was originally going to buy Allen a costume like Mana's - to bury him and Allen spent most of his time mourning over it and the only family he had ever known.
After the death of his caretaker, Mana, Allen tries to call him back with the aid of Adam, pulling his body out of rest to make a golem he learns later is an Akuma. The Akuma goes insane and starts to attack Allen but before it can do more than injure Allen's left eye he is rescued by his first Summon - Cross Marian. The world of Summons is unknown to the young boy so Cross raises him as "best" he can (including debts) after Allen pulls out of the shock of what happened. The debt-producing man teaches Allen about the Summons, gives him Timcampy (a guiding Summon that stays out), and tells him of the Faithful. But as a result of the conflict with the Akuma, Allen's brown hair becomes a shocked white, he receives a tech-prosthetic eye, and the back of his tech-prosthetic hand grows to about the size of a
grapefruit but still has free range of his fingers. There's a huge jewel on the back of his hand the same gray color as his eyes.
Allen is fifteen when Cross disappears into the jewel on his left arm, but before he does Cross tells Allen to go to their headquarters, that he'll be of use there but keeps the prophecy to himself as he disappears into Allen's tech-prosthetic arm. There he'll remain until Allen is strong enough to Summon him seeing as Cross' strength is not one to take lightly at all. The prophecy was thus fortold by a very powerful Summon (Hevlaska):It is said that one day a group of people with powers will appear and the earth would begin to break. But there would be a light, a person with an arm and eye not his own. And at his side an army of people to face the would-be destroyers of our world. Only with their help would the Chosen One be able to save the earth from destruction.
After settling Cross' debts, Allen goes off to a far away city where the Faithful are said to "keep shop". Along the way he performs to procure meals for himself and for Timcampy, collecting a piece of magic along the way that Timcampy swallows for safekeeping. However his first "friendly face" at the Faithful's headquarters isn't friendly at all, Kanda almost beheads him before Lenalee stops the swordswoman. Once inside he meets Komui (Lenalee's brother) and the two Summons agree to be called upon by Allen, Komui explains again what they do but nothing of the prophecy once Allen speaks of Cross.
Komui sends Allen out to an ancient and deserted city with Kanda's aid to retrieve more free magic. Everything after that continues like normal, his second mission is with Lenalee where he meets a new Summon (Miranda) and fights with his first Blessed (Rhode). His tech-prosthetic eye needs to be replaced and its replacement has an AI secreted within it, not that Allen will learn of it anytime soon. Bookman and Lavi meet up with him while Lenalee is recovering and accepts the contract as well. Lavi and Allen meet yet another Summon (Krory), then the journey to a continent across the seas for rumors of a very powerful Summon being held captive there by the Blessed.
Marie and Daisya also join the ranks of Allen's Summons before they head off with Kanda on their own mission to bring back another powerful Summon named Tiedoll. It's during this mission of the others that Allen realizes that he can sort of tell in a general sense (direction) of where the Summons he has a contract with are and if they're alive/well. Leaving Miranda behind Allen heads off with Bookman, Lavi, Lenalee, and Krory on their own mission but just before they can board a Faithful-supporter's ship that will take them to the island continent a Summon makes itself known to Allen. Tyki (Blessed; having already killed Daisya) is in the process of watching Suman Dark dying after being separated from his magic, a huge explosion that Allen tries to save the Summon from but is unsuccessful.
Allen is dazed after the explosion and Tyki takes the opportunity to try and destroy the Chosen One. He puts a hole into Allen's heart and severely damages the tech-prosthetic arm, leaving him for dead in the ruins of the city. Lavi and Lenalee only find his bloodstains on the orange dirt and decide they have to go on without him, Miranda joins up with them and they ship off. Allen doesn't die however and wakes to find himself in another building deep underground that belongs to the Faithful, his arm missing.
Bak (the head of this branch) enters the room not long after he wakes up after Allen finds he's too weak to get up out of bed, not to mention Fou asleep on his leg. The Faithful explains to him where he is and that his group has gone on, it's Allen's job to get better and to later train with Fou as Bak and his team try to repair the damage done to his tech-prosthetic arm. Allen doesn't even question why it can't just be replaced, he'd much rather have the same one back, it's special to him in ways he doesn't understand.
Weeks and then months pass as Allen heals and begins training with Fou, Bak is having a hard time figuring out exactly how to fix Allen's arm. They can't get it to connect properly to the tech-prosthetic base that was build into his shoulder, almost as if it is being rejected. Daily attempts are made to make the connection yet it seems more and more impossible to achieve until the Faithful's underground facilities finds themselves under attack. Defense mechanisms kicked in almost immediately but are plowed through as the powerful Akuma keeps searching for Allen, somehow the Blessed found out that he was still alive.
Fou decides to go out and distract the Akuma while everyone else stays hidden behind the last wall, thanks to the time that she bought Allen and his arm finally connected properly. Bak, of course, gave his tech-prosthetic upgrades so that Allen could pull it out into a thick blade coated with the powers of the Summons still within the jewel at the hilt - a weapon capable of destroying golems and Blessed.. Allen destroys the golem with the new blade and takes the same route back that it had come through, his first journey through the Ark though at the time it's still under the control of the Blessed. He finds himself outside suddenly with the Summons that had gone on ahead without him and those that had gone off on their own separate journey. But they are not alone, they're fighting several of the Blessed that are also on the island, Kanda and her group newly arrived as well.
He joins in the fight only to have it suddenly end with a flash of light, and everyone starts to regroup instead. But while Allen is checking on everyone a hole opens up under Lenalee, Allen grabs her and is pulled through creating a sort of chain reaction. Lavi, Kanda, Krory, and a shipmate named Chaoji are all pulled through as well. They all find themselves within the Ark and Tyki shows up long enough to challenge them to find their way to the top before the area they're currently in is destroyed. The Blessed leaves them with a key and the group begins trying to find a way out.
They first run into Skinn, Kanda stays behind to deal with the giant Blessed and their group splits further again when they make the acquaintance of Devit and Jasdero, Krory stays to hold them back and hopefully help Kanda through. The remaining four keep moving up a grand staircase in order to find the exit or a way to save everyone. But at the end of the stairs they simply find Rhode and Tyki waiting them. Allen gets his kiss from Rhode and goes off to attack Tyki just like normal, leaving Lavi with Rhode.
It's a long and difficult fight, but Allen pulls out his sword and slashes at him with it. The magic of the Summons coating it reacts terribly with his Blessing and Tyki is out for the rest of that fight as Rhode unleashes a temporarily brainwashed Lavi on Allen. His friend breaks through her words and comes back to him just in time as Tyki reawakens and goes beserk on them, Allen and Lavi start fighting him since Lenalee's legs are too damaged and gain Chaoji's help when his magic finds him in the Ark. For the first time Allen is strong enough to call forth Cross, a powerful enough Summon to fight and possibly win against Tyki. Allen he sends to the room where the piano is, where Timcampy is waiting and calls everything back.
Tyki is gone when they all regroup, surprised to find that the device that allowed the Earl to create his Akuma remains inside the Ark and thus within their control just like the Ark itself. Using its abilities Allen gathers the rest of the Summons waiting on the destroyed island and they all head back to their original headquarters on the other side of the main continent. For a while everything goes back to normal, Allen and the others get sent on missions and more powerful Summons are added to the gem on his hand. But Allen is to have someone (Howard Link) new joining him, someone that is under the control of and reports to another faction of the Faithful - the Silent Ones. All because during Allen's playing of the piano - something Allen didn't know how to play - there arose a shadow from his left. But the "public reason" is to ensure the safety of the Summons in the face of this unidentified and unknown AI (artificial intelligence) program somewhere in Allen's prosthetics. Detatching either from his person is denied because of the prophecy and Allen's importance.
The very next day after Link is placed in charge of Allen and the others, the headquarters falls under attack by one of the Blessed that somehow snuck in. She is sent with the purpose of retrieving the device that allows the Earl to make his golems. Allen rushes into the fight, but he's too late to stop Lulubell from escaping with it until Miranda uses her magic to call it back. However the others have to deal with all of the powerful golems that the Blessed brought with her and most of the headquarters is destroyed as well as compromised because of this. Allen and Lenalee start to fight against one of the most powerful golems they've yet to face after Lenalee's boots alter themselves yet again, becoming a part of her. They had somehow locked-down and she couldn't use them until during the battle. She asked the magic to help her save her friends and loved ones, in return she'd give everything she had been holding back to the war. What was once a weapon for her to summon became anklets that transformed into boot-like weapon, always with her.
It takes the two of them plus the aid of Cross to finally rid headquarters of the last golem, but seeing as their base is no longer safe it's time to move. It takes them a while to pack up everything and only have a few misshaps before the Faithful settle into their new building three cities away from the old one. Apparently even after setting a "guard" on Allen and the Summons, the Silent Ones are not yet done with him; he, Lavi, Bookman, and Komui are pulled into a meeting with the head of that faction: Leville. After a brief discussion, Lavi and Allen are sent into a room filled with Silent Ones that entrap the Chosen in a set of barriers and Lavi has been told to do nothing but listen. Cross informs Allen of the prophecy and what he knows of Nea's presence in the tech-prosthetic eye of Allen's.
Cross had come across it in his travels, knew of the AI it possessed and planned on planting it within his own head until he happened across the Chosen One. Allen received the eye after his own was destroyed fighting Mana. No, he doesn't know all that the AI can do - as of yet the name Nea is unknown - aside from controlling the Ark. Which means that the Blessed will come after Allen now to destroy it or capture it. And that there's another danger to having an AI program inside a tech-prosthetic, no matter the other advantages, after a while the AI starts to exert its own personality over that of the user's. It wasn't a part of the prophecy so they don't have any idea what it'll do should the AI take over Allen, but typically they end up killing someone the user loves so there isn't a tie to them.
Allen refuses right then and there to allow anything - let alone an AI program - to take over him and keep him from his path. The next morning Cross is suddenly gone from the gem and Allen finds that he can no longer Summon him, bereft without his mentor Allen is listless when his disappearance is announced to everyone else as well as the fact that there is an AI in Allen's tech-prosthetic eye. Komui asks them all to attempt to pull the eye out of Allen should the program attempt to take over him or if it should fully take over. Destroy it. They don't need the Ark to win the war against the Blessed after all.
After a few more missions - in which Allen becomes comfortable with and used to Link's presence - Kanda is sent with him to one of the more elegant cities where a string of peculiar robberies have cropped up. And somehow snared a few of their comrades, for a few moments even the three of them become victims of the same affair. Finally they track the magic user down to an orphanage and a child that wanted to protect his only home from closing down. They're trying to collect the child (Timothy) or at least the magic that he's using (he's much too young in Allen's opinion to form a contract with) when the orphanage falls under attack by several golems that somehow found their way in. Allen, Kanda, and Link are left to fight and protect the innocent people caught in the middle of the fight when another powerful golem appears, one just like Allen and Lenalee fought.
Timothy joins their fight, moving alongside Link to defeat the weaker ones (but still almost as strong) while Allen and Kanda fight the most powerful one. It manages to give them a run for their money and the golem almost defeats Allen who chooses that moment to call the sword back to him and it pierces them both. It catches the golem off guard and then Allen as it allows Nea a bit more wiggle room in Allen's head, the eye flashing yellow and catching the Earl's attention miles away. But the moment is gone when Kanda charges in, between the two of them the golem is destroyed with a matter of pulling blades. Battle over, the trio take Timothy back with them to the Faithful's new headquarters and Allen forms a contract with him.
A week or two passes and suddenly the Faithful are playing host to more Silent Ones, only these aren't of the same caliber as Howard Link is. They've been altered somehow and are now capable of using the same kind of weaponry that golems do. It seems that they two are going to be joining the Faithful in their quest at the behest of their commander Leville. A few more missions pass by with these new "players" and yet again everyone is separated from Allen's side except Kanda's. They separate for a few minutes and Allen finds himself surrounded by Blessed, Madarao and Tokusa (two Silent Ones) with him get into serious trouble, the latter being injured by (the new and improved) Tyki Mikk.
Allen launches an attack against him, leaving Madaro to deal with one of the other three, the third disappearing with Tokusa. The fight with Tyki somehow launches them both to the location where Tokusa was taken and most of the other Blessed and the fight is interrupted by Nea coming out when the Earl confronts him but Allen shoves him back away. Allen finds that most of the scientific team from his own branch of the Faithful along with several other new faces. Moments later Kanda awakens from the injuries that she sustained from her own fight with another new Blessed named Wisely. Apparently the Earl's plan was to use Kanda to somehow wake up someone Kanda firmly declares as "dead", Alma Karma, even with the boy's body right below her feet. A brief fight and somehow the two get sent back (along with Rhode) to relive Kanda's memories as a young child in order to wake up Alma again.
Allen finds himself watching the artificial birth of the twins, Yuu and Alma, which is really just a pool among numerous other pools. Each of them appear to hold two children, sleeping until they're born and look to be about nine years old, born with hidden memories of Summons who had died in battle. The two bicker and fight like demons though it seems that Alma is the more docile and friendlier of the two and when they're not fighting each other they're fighting with magic being forced on them. The repeated experiment to force the bond between child and magic ends up torturing their bodies and sometimes ending their lives, but somehow they reanimate. Allen and Rhode watch the history of these two children unfold, Allen with growing horror at what his comrade has gone through and tries to intervene when it comes to the point where Kanda is repeatedly killing Alma.
And his intervention happens out where the others are waiting for Alma to awaken with the prompting of Kanda's memories: Allen raises his left fist and punches her right in the middle of the forehead, shattering the spell. But it's too late, Alma has reawakened and so has his rage at Kanda, at the people who had done this to them, everyone around them were participants in this. Unfortunately the altered Silent Ones have genes from Alma inside of them along side the device that allowed the Earl to create his golems, Alma's genes make them go berserk. Kanda finds herself fighting Alma again and Allen faces the mutating Tokusa after he helps save everyone of the Faithful from Alma's original blast of rage. It is a fight that Allen doesn't want and he focuses on trying to get Tokusa to get a hold of himself, to hang on so they can fix this.
The Earl however goads Allen on with saying that the AI would be able to take care of things if Allen just let him out. Something Allen refused to ever let happen but he has to do something as the fighting between Kanda and Alma escalates. Bak Summons Fou (she's a special sort of Summon like Tim) after Allen gets injured and she helps defend him from Tokusa's attacks while he tries to figure out exactly that, it's evident he has to stop Kanda. But Allen couldn't save Alma like he normally did with the golems, the rage was simply too strong so at the very least he had to stop Kanda from killing her twin. A twin that started attacking Allen because he registered as an enemy and Kanda herself had started attacking her Summoner.
Using her speed Kanda attacked Allen and struck true, her blade in one way and out the other as Allen still tried to talk sense into Kanda, that they should make up instead of seeking to destroy one another. The damage is done to Allen however and the magic succeeds in driving the necessary wedge in Allen's subconsciousness and allows the AI out of Allen's eye. Allen passes out because of the wound very briefly, finding himself chained to a chair and face to face with someone vaguely resembling Tyki, but when he mentions the name he gets one instead: Nea. Timcampy feels this change miles and an ocean away, carrying Link and Tevak to where Allen and the others are on another continent, breaking the barrier that kept Allen's tech-prosthetic eye from working correctly.
And breaking the barrier allows Allen to regain control of himself, to shove the AI program back in its technological cage and realizes whom Alma's past life was. The ghost that had haunted child Kanda's days, the memories of that past life peeking through, and cries at him to stay quiet about it. Alma initiates a self-destruct which ends up destroying most of his body and ruins the regeneration of Kanda's body. Allen helps the two of them escape - though Kanda's magic separates from her and is left behind - from the Earl and his Blessed, from the Faithful and their wrongful experiments, and finds himself fighting Tokusa again when Fou's Summon-stone breaks. He tries once more to save the Silent One but is bound upon Link's arrival, gets attacked by a similarly enraged and mutated Tevak but gets saved by Timcampy.
The Earl takes his leave of the ruined building, mutated Silent Ones at his side thanks to Alma's going beserk that put them in his control with the device parts in them. Allen is bound and chained, his arm locked down and kept in the prisons of the Faithful's headquarters after releasing all of the Summons that he had left in the gem which wasn't very many at all. The reasons for this arrest? For aiding in the escape of Alma and Kanda, for attempting to kill the Silent Ones who were mutated, and for the AI's full awakening of his person. He refuses to eat during his imprisonment in what had once been his home he's left with nothing to do but think, especially when Link tells him that the other Silent Ones - the altered - had been his family as a street kid.
Allen wonders how many others he's failed to help correctly because he's been blinded by other emotions, a break in his mental armor that Nea grabs and tries to take over Allen yet again. He's visited by a man proclaming to be part of the Faithful - in a powerful position really - and somehow the man tries to meld with Allen and his bound left arm. It's interrupted by Link and the Silent One is temporarily taken care of by the visitor in such a way that Allen flat out attacks him, thinks he kills him. But finds himself face to face with a creature called Apocryphos, something that feels like corrupted magic, and who tries melding with him again. Allen sees this thing attacking Cross in his final moments before the powerful Summon disappeared from Allen's gem permanently.
Tyki and Rhode appear before this could get any further than it did - Allen's arm already a wreck from the attempted melding - and Tyki jumps into the fight as Rhode frees him from his chains. But as soon as Allen is free and Tyki finds himself pinned by Apocryphos, Allen charges him enraged for the false Summon attacking his mentor. Opponents switched Apocryphos starts to attack Allen but Rhode jumps in the way, taking the punch and is knocked out. Link takes the moment to make himself known as still being alive and busts Allen and the Blessed out of the prison, Timcampy flies them all out of it and out of Apocryphos' reach. Tyki leaves Allen and Rhode to escape while he covers their escape, saying that Allen has two powerful monsters inside him that sow chaos wherever he goes.
Allen is left confused with the unconscious Rhode who wakes and tells him to keep on walking ahead then disappears. Left by himself Allen wonders what to do next and even as he decides to go off in search for Cross - part of him knows he's still alive - Lenalee appears and tries to reason with him. But he has to leave and tells her that he'll always love everyone in the Faithful and it's always his home before disappearing in the Ark and heading toward Mother's. His road would always be parallel to the Faithful's, he would always try to work toward the positive end even if his family had to attack him if they met again.