Shadow Dragon's Power

Yuji is the weakest and has been teased and beaten by his clan members since he was little.
But one evening he gets the power of a dragon and his whole life changes.
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Many thousands of years ago there was a battle in which the four dragons united to defeat the fifth dragon. There is a Water Dragon, a Fire Dragon, an Earth Dragon and an Air Dragon. The Fifth Dragon is called the Dragon of Shadow or Shadow Dragon. The Shadow Dragon was considered the strongest of the Five Dragons. Each dragon has its own clan. These clans are family clans. After the four dragons defeated the Shadow Dragon, they were very weak. And at that time, five families took care of the dragons. After the dragons died, their power was transferred to the elders of the families and the clans were formed. The clan heads are worshipped like gods.
Each family has a huge castle. What stands on a mountain. He the mountain under the castle lies with all four mountains the dragon core. A huge glow of crystal that supplies the people and surroundings with magic.
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English is not my main language so mistakes can occur