Ive done some reaserch and found very little to go on about this gruop.
Most trails led to a game called fire emblem for the GBA. In this game the black fang was a guild of assassins....but they only targeted nobles and offiacils that abused their power, until someone took over and used its reputation as a cover up for their true intent ( i have no idea about half the stuff this game was talkin about lol)
anyways, i heard about their used to be a similiar guild by the same name on the Korean server of elsword.
it was said to follow a similair purpose as the original black fang. But the guildmaster died, yes in real life, and the guild fell apart, different sides fighting for control.
i think they said it was disbanded butidk for sure i dont know how to go to korean server lol
oh yeah when that unknown user said that thing about "bitten by the black fang?' thats was ......i guess like a warning saying "im coming for you!!!" lol
anyways theres ur info saber