Just read the Hunter X Hunter spin-off one-shot of Hisoka's origin by Ishida Sui, the author of Tokyo Ghoul..
it was pretty interesting, but it looks like he tried emulate Togashi's simplistic and crude art-style e.e
i mean, Ishida's art isn't really very refined, but it's heavy on screen-tones and texture, which the one-shot was very lacking in
anyway, it still wasn't much of an origin, since it just followed where he learned his nen and stuff, not where he came from or who he really is
but it's definitely still worth a read if you can get over the art~