Kharlan War

The Ancient War is a conflict shrouded in mystery. It is said to have been a confrontation between two powerful countries, but few records remain of either countries. The war is said to have started approximately 5 000 years ago and lasted for 1 000 years. It was ended by Mithos the Hero in the Holy Ground of Kharlan by making a pact with the Goddess Martel to seal away the Desians, who were the reason the war existed. However, the legends say that by doing this, Mithos the Hero sacreficed himself.

The truth
Muth later in the game, it's revealed that the Ancient Kharlan War was actually a war against the two kindoms of Sylvarant and Tethe'alla. In fact, the Desians did not exist at all at that time. Mithos Yggdrasil, the great hero, is revealed to have been a half-elf, and together with his sister Martel, a fellow half-elf named Yuan and the human Kratos, they managed to stop the war by making pacts with the Summon Spirits. However, right after the war ended, the group was betrayed by an unnamed human, and Martel was killed. This broke Mithos, and he told Origin to make him a sword capable to manipulate creation and time itself; the Eternal Sword. Then he used the Eternal Sword to separate the original world into Sylvarant and Tethe'alla. Having broken his vow, Mithos forced Origin to continue having a pact with him by sealing him inside Kratos, making Kratos' life and the Seal of Origin fusion together; should the Seal break, so would Kratos, and vica versa. Mithos then created Cruxis on Derris-Kharlan in order to find a way to revive Martel. The leaders of the organization were called the Four Seraphim, being Mithos himself, Yuan, Kratos and Martel as the fifth. They found a way to become angels and stop their physical clock, and lived for four thousand years, trying to revive Martel through having the Chosen from each world to go through a Journey of Regeneration.

As time passet, the people from both worlds becan concidering Cruxis as heavenly messengers of the Goddes Martel.