Kanda's canon history and backstory [FOR META KNOWLEDGE ONLY]
In many ways, Kanda's past remains so veiled that it's hard to summarize it at all—information about his history has only recently begun to be revealed.

What we know for certain is that Kanda became General Tiedoll's pupil when he was nine years old and that he traveled around the world with him for a year before arriving at the Black Order Headquarters.

What happened to him before this, however, is open to interpretation: Asian Branch chief Bak Chan calls Kanda a "synthetic disciple," apologizing to him for the Order's ill judgment when they made him and, seemingly, others like him. Bak also speaks of a tragedy nine years ago—one that seemingly involved Kanda in some way, and which would have taken place when he was around the age when he first met Tiedoll.

These apologies come alongside the revelation of "Third Exorcists"—synthetic people of another sort who have been produced as human-akuma hybrids through the manipulation of akuma DNA. Kanda, seemingly, is the product of a project that came a generation before: Bak Chan and Renee Epstein's attempt to make a group of synthetically generated "Second Exorcists."

Because only those individuals who are compatible with Innocence may become accommodators for it, making their numbers necessarily small, the goal of the Second Exorcists project was to somehow create compatible users from scratch, thus swelling the ranks and gaining an advantage in the war against the Millennium Earl. Though the exact mechanism used to create Second Exorcists is unclear, recent chapters speak of a material (or possibly a being) called Alma, a name which clearly has resonance for Kanda. Since the Order had already tired and failed to simply implant Innocence into incompatible users and force them to synch with it (the tests apparently resulted in at least one child's death), it seems possible that the Second Exorcist project may have attempted to somehow manipulate genetic information in some parallel process to that by which they later make the Third Exorcists--using Alma along with some other material to synthesize life.

However it was all accomplished, Kanda was the result. Insofar as he is a capable, dutiful fighter loyal to the Order, the project was a success. Not that there weren't glitches—for one, Kanda sees illusory flowers: a lotus that he keeps under glass in his room, and at times others as well, falling all around him like rain. But this seems a relatively minor concern for an organization fighting a war for human survival, and whatever "tragedy" Bak referenced to Kanda, it seems unlikely that a little boy seeing flowers that aren't really there would be enough to make them halt a project that could let them generate an army of elite fighters in place of the dozen or two they would have otherwise.

Something disastrous must have happened to result in Kanda being the only product of the Second Exorcist project. What the catastrophe was has yet to be revealed.

At any rate, it seems clear that Kanda has spent his entire life with the Order, that he was created to be an Exorcist, his sword, Mugen, crafted for him by Old Man Zho (seemingly a kind of confidant for him when he was a child—he was the one who first told Kanda to keep the illusionary vision of the lotus he sees everywhere a secret), and that he has never known any life but that of a warrior and Black Order member.

This does not mean, however, that Kanda reveres the Order or embraces the religious framing which they assign their conflict—he tells Bak that he doesn't give a damn about the Order and when a Vatican representative accuses him of being disrespectful to God, he tells the man to shut up. Whatever Kanda's motivation for fighting, it's more complicated and more personal than slavish obedience to the religious faith that made him.

Of the many foes he has faced in his life as an Exorcist, Kanda has managed the considerable feat of defeating a Noah—the supposedly-immortal clan who claim descent from the Biblical Noah himself—making him the only Exorcist to have accomplished such a task. This battle, which takes place on the Ark during its disintegration is won at great cost to Kanda: Mugen is shattered, his life force is deeply drained, and he doesn't escape the room before its collapse around his ears. However when Allen reconstructs the Ark before its final destruction, he also reconstructs the room from which Kanda had failed to escape, and the swordsman is thus effectively saved.

When Kanda subsequently finds himself without Mugen during an attack on the Order HQ, he uses whatever swords are available to him to fight the intruders, places his body as a shield to protect Supervisor Komui Lee from the Level Four's attack, and is willing to stand against the akuma even armed with only mundane weapons that will be useless to harm it.

Despite his constant antagonism with Allen Walker—the two have been like oil and water since their very first meeting—Kanda is willing to fight at Allen's side when needs must, as is the case when the two of them, along with Noise Marie, are sent on a mission together to investigate the detention of a group of Finders by local police. When they find themselves sealed into an orphanage with no way out and with another Level Four akuma to defeat, the two manage to destroy their foe by both impaling it on their swords together.

In the course of the battle, however, Kanda and the others become privy to the knowledge that Allen's sword, which is supposed to only harm evil, does damage to him as well.

After that battle is finally won, the Exorcists are again dispatched around the world, Kanda being sent to Jordan where he is confronted by a mysterious figure who is allied with the Noah and who has apparently been looking for him.