THE LEGEND OF DRAGON WARRIORS
The existence of the dragon warriors came when Hiryuu was to be persecuted by the humans and before the founding of Kouka. The four dragon gods tried to help Hiryuu from danger, only to be shunned by him as he loves humans despite their flaws. Because of this, they looked for humans to be their counterparts and granted them their own powers when they made them drink their blood. From this, the first dragon warriors came to the aid of Hiryuu and their land. Together, they founded the five tribes and led them to wars against the neighbouring countries. After the death of Hiryuu, three of them, namely Hakuryuu, Seiryuu and Ryokuryuu, established their own villages and lived there silently to protect their existence from people wanting their powers and to preserve their bloodline. Ouryuu remained in the Hiryuu Castle and became a priest in order to guard Hiryuu's family and keep check on the affairs happening on Kouka.
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Well this is the known Legend of Kouka, but throughout the years, people had forgotten the other Legends of Pheonix, Kirin and Tiger.
After The Dragon Warriors existance, the Pheonix God, Kirin God and Tiger God also give their blood to the humans to help the dragon warriors protect King Hiryuu. After decades of war, only 1 left from each of the species which is the Flame Pheonix, who controls the flames and can see through the truth , Jade Kirin, who jump through the sky and speed through the wind and the Mist Tiger, who have the teeth that bite through everything.
But the records of the legend is too limited that peoples had forgotten them eventually....