Ultimately what happens is up to GM and player, but here's a condensed version of Armiger's backstory, and other Grail Knight stuff I've done so far. Use as-is, retcon, or rewrite to taste. The Knights are a loosely structured, international paramilitary organization. They have three recognized ranks (Aspirant, Squire, Knight), recognizing that above a certain level, there's no further need for authority: their "badge" (Excalibur) intrinsically weeds out the unworthy. Their tool of choice is the sword, but they'll use modern guns, armor, and other tactical gear to get the job done. A typical teenager in Masks would be an Aspirant or Squire rather than full Knight. Promotion to Knighthood is social, and involves ritualized combat. This would be a key moment for the character, opening up after a successful Moment of Truth or unlocking advances below the line if it hadn't emerged from the fiction some other way. Armiger got promoted to Squire in a cutscene, so has one trial to go. Armiger has a potential love interest in the form of Jaycee, but although we've written her as someone who's grown more interested in him, his own feelings are unstated (he asked her out awhile back, clumsily, and her pride still smarts from that, but we haven't heard from him since). As well, we don't know anything about his own family, how he got the sword to begin with, or other key details, so there's a very large map with a lot of blanks to fill in. The Protege An obvious power to have is "impossible fighting skills". It's too soon to say just what Armiger's specific focus is (his teleport spam is neat, but not the whole story). There's a few potential mentors to adopt: Lucius (his teacher as an Aspirant and still a source of information), Skinner (his current trainer), or even a goetic daemon or some other mystic figure. It's possible that one of the mystics on the HHL has taken an interest - like Tatanka, a figure that Alycia wants respect from. Mentor's resources are trickier. The team has a hidden base and communicators (basically), but surveillance equipment, false identities, and security systems might all come from the military side of the Knights. The Soldier In terms of what they do on the playbook, the Grail Knights are a direct drop-in for AEGIS with no revision necessary. They'll give orders, supply equipment, and provide training. "Your superiors" are experienced knights like Skinner, and could be anyone from around the world, but otherwise work the same way.
