The Sapphire Dragon originally lived within the primeval Wild Forest and had done so for nearly three hundred years until it met Anderson Sapphire, the ancestor of the current Grand Duke.
Anderson was a very charming knight. As a Marquis of the Blast Furnace Fortress Kingdom, he owned vast lands, including the habitat of the Sapphire Dragon. In order to ride the dragon, Anderson continuously used various resources to please the Sapphire Dragon and ultimately hit its G-spot.
He gained the opportunity for a mind battle.
In the mind battle, he succeeded at once and gained the Sapphire Dragon's recognition, becoming a Dragon Knight.
When he applied to the Blast Furnace Fortress Kingdom to establish a duchy within his territory, he was rejected by the royal family at the time and had to search for new territory. Thus, he chose an uninhabited wasteland claimed by the Eagle Kingdom for his nation building. He had thought the Eagle Kingdom wouldn't turn hostile over a piece of wasteland.
