There is a war that rages across the realms between celestials and fiends called the Forever War. Legend says that the Forever War will never end until conditions are met that will be given to the world by a being known as 'The Prophet.' In this war Asmodeus the Fallen and his fiendish hordes seek to conquer all realms, freeing all from divine expectations calling all to a higher standard. In his delusion, he believes he brings the dawn, the morning light that illuminates the truth; that grace is a trick of the divine, mercy a lie, and forgiveness an illusion. These things instead place upon all so ensnared by these false promises a prison of impossible expectations towards which they labor but can never attain.
Conquest of the Realms
From his prison of Hell, Asmodeus sends out his hordes to conquer the realms, to establish a new order wherein all have the freedom to satisfy their every whim. In this new order nothing is sacred and anything goes. Acts of murder would be as acceptable as acts of kindness, and the right to impose your will upon others relies only on your capability to do so. Should the fiendish horde find a foothold, doorways are established that connect to hell, and the power of Asmodeus' twisted mind quests forth driving a chosen general that brings corruption in its wake. A conquered realm is forcibly changed by the presence of the fiendish horde into twisted perversions of what it once was. Pristine lakes may become poisonous waters, docile fauna may be transform into aggressive predators, flora may mutate, creating a region inhospitable to life.
The Heavenly Host is the standard raised against these fiendish hordes. It is through their tireless sacrifice they keep Asmodeus twisted "truths" at bay. It is through their efforts that conquered realms are reclaimed, corruption is cleansed, and realms are returned to their former glory as intended by the divine.
War in the Prime Realm
The forces of Heaven and Hell are both forbidden to bring their armies into the Prime Realm. By divine ordinance, the Forever War is not to be waged there. Yet in times past the both Asmodeus and the Heavenly Host have used other means to influence events in the Prime Realm. The methods for doing so varied widely. At times those capable of doing so would use their arcane abilities to randomly contact those of another realm, sometimes a fiend, and other times a celestial. Such contact was often used as a means of gaining favors in exchange for guidance or information provided to those calling upon them. Other times sentients in the Prime Realm meddling with far more powerful uses of the arcane would themselves open gateways and compel a fiend of celestial to their side. In every case, the influence of such forces is inevitable and often culminated in events that impacted entire regions, continents, or worlds.
The Half-Bloods
The first half-blood was the result of one such meddlesome affair. A Wizard named Thais Arruda of the Begundi Isles, desperate to save her tribe, summoned Agirez, a powerful fiendish lieutenant who promised to give her knowledge of a spell capable of saving her people. The price was her affections. Desperation robbed her of sense, and she agreed, breaking the wards binding him to the summoning circle. Agirez raged forth, striking her people with flame and rage, leaving only Thais alive, after which Agirez impregnated her, and retreated home. It is said that the madness of that trauma sustained her until the day she gave birth, but seeing the crimson skin and small horns of her offspring drove her over the edge. History has no record of whatever came of Thais, but it is said that Mad Thais raised the child for a time until it ate her and was driven to hell by a celestial.
From that moment on, Tieflings have been used to take advantage of a technicality of the divine ordinance forbidding demons and devils access to the Prime Realm to attempt a quiet conquest through the use of half-bloods. Not technically a fiend, nor yet any other race, it was discovered that few of their number can often escape notice in the Prime Realm, if only for a time. They work on Asmodeus' behalf, using their abilities to seduce or entice others to perform tasks to sinister ends. The first such occurrence culminated in the war between the People of the Sands, and the Ashtubai, which required the intervention of the Taur'Amandil and gave rise to the creation of the Aasimar as a counter to the Fiendish half-bloods. Since then Tieflings and Aasimar have served in the Forever War as footsoldiers, mages, healers, and often carrying out assignments where their more powerful pureblood counterparts may not tread.
