The Cosmic Dragon

A servant inside a castle. They may go completely unnoticed, no matter how many of them actually exist. They work diligently, in the shadows, always there but never actually seen. The people they serve hardly notice the people behind the clean halls, and made beds. They are loyal shadows without a name.
Keiran has served inside the walls of Kouka Kingdom starting at the age of 6. Watching and caring for the royal princess without even a single thank you or glance. He hardly existed at all despite his constant presence in the young lady's life. Not even the Thunder beast paid him much attention, after all, he wasn't all that extraordinary.
Keiran was a mere servant boy after all. One that wore a mask, so even his face would have been familiar to the eyes of others.
However that changed the night of Yona's sixth birthday. The night, where Keiran stepped in and gave Yona and Hak the escape route they needed sacrificing himself in the progress. At least, that is what Yona and Hak thought.
Yona has gathered the four dragons... White, Blue, Green, Yellow. It is time for her sword and shield to appear; The sword and shield coming in form of a supposedly dead servant. The servant Yona and Hak could never get out of their minds.