so imagine like. you have this coworker. and hes an asshole in general, you dont like him, nobody else likes him. but the relevant thing is that he is just really, really into arthurian legend. very into medieval literature, very into the post-roman anglo saxons, doesnt really strike you as the nerdy type but he knows a lot about it. he spends a bunch of work hours researching allegedly arthurian artifacts, and even pulls rank and convinces one of your other coworkers to also research this stuff (by lying and saying one of the higher-ups wanted it). in fact, he claims his entire motivation for working at this job is that your boss has promised to give him an actual 5th century sword. but it's like. you dont know how much of this to take seriously. it wouldnt be out of character for him to be entirely bullshitting you. so whatever.
and then after you quit and the company falls apart and you think youre never gonna see him again, you find out that your asshole coworker is, actually, Sir Lancelot, and him working at that job was all part of his preparation for the return of the actual King Arthur.
that would be the experience of everybody who was in Organization XIII finding out that Xigbar is Luxu.