/canon dump
Well... [Komui sits back, smile almost vanishing] It's an old story. Seven thousand years, in fact. So I'll just hit the highlights, hm?
[He's told this story many a time, to all the new recruits, so there's a practiced feel to the speech.] At the time the Old Testament refers to as the Great Flood, our war began. An ancient substance was used to defeat the Noah family and their leader, the Millennium Earl, in a battle so great that the Earth was destroyed. We now call that substance Innocence, and it opposes the Noah's Dark Matter, the substance from which they derive their powers.
After the battle, the Innocence was left behind for us to find and use when the Earl returned, as was prophesied. Our Exorcists are able to synchronize with the Innocence and use it against the Noah and their weapons, Akuma. [he'll... get into Akuma in a moment. It's a rough thing for people to hear.] Innocence evolves over time and according to the will of its user, and Dark Matter evolves similarly. Only Innocence can stop Dark Matter; that's why all the restrictions around anyone but Exorcists fighting the Noah.
There are fourteen Noah in total, although only a few of them are here, thank goodness. [Four if you count Allen, which is why he's not giving a number. And because he's being a bit more general here on purpose, with a smile,] We know less about it than we do about our Innocence, of course. They do the Earl's work to try and put an end to humanity. Each of them has a unique ability from their Dark Matter. Tyki can touch -- or not touch -- anything he wishes, Road can trap you in a dream she has control over.
They're extremely dangerous to everyone here.
[And glancing up, because he's not inclined to go into specifics quite yet. But that depends on what Reid wants...]