GM Worldbuilding Session #1!
The Custodians are somewhat a cross between Full Metal Panic's MITHRIL and Evangelion's NERV. Officially, they are an independent organization are funded by the United Nations to act as a specialized response unit to problems that conventional military tactics and force cannot hope to subdue, containing both military and civilian branches. Unofficially, they hold a lot more power than most people think and are responsible for releasing "safe" technologies slowly into the world to improve overall life since they field experimental black box inventions created by geniuses decades ahead of their time (and also profiting greatly off these patents so as to achieve the greatest independence possible).
Though publicized, very few realize the true extent of the Custodians' might and influence and their inner workings highly secretive, on par with Area 51 or the Illuminati. Despite this, they are also a haven for "nails that stick up" and recruit the best in their various fields despite personal quirks and backgrounds, much like the Nadeisco's Nergal, all the while offering a high degree of freedom unheard of compared to most other secretive organizations. Even their name was picked to be as innocuous as possible so as to provide both the public and their enemies with the assurance that they are just one of other such similar minded organizations out there.
Their antithesis is a group dubbed QLIPHOTH, ruled by a mysterious council of ten that regularly incites wars across the world (and sometimes even guiding alien invaders to Earth) for "fun and profit". They have enough power to erase small countries over night and supplies arms and forbidden tech to the worst of the worst, perpetuating a cycle of violence solely for amusement value sometimes even. They are cancerous and whisper sweetly poisoned words into the ears of the movers and shakers of the world, tempting them into darkness. Employing any and all means to achieve their goals, QLIPHOTH has since time immemorial planted the seeds that would spring forth the worst tragedies to ever happen across mankind's history. Why they do this is anyone's guess.
More to come later.