I knew an enemy that fit the riddle perfect. A supplicant. "Something burning me from the inside?" Simple: explosives. "Have to get it out?" Simple: explode. "We are everywhere?" Simple: lots of supplicants. "The darkness forged me?" Simple: supplicant is an enemy. "I must protect my home?" Simple: supplicant is defending its home. "I lost the fight?" Simple: VoG Atheon fight.