Serafina and the Key to the Egg

In a hidden away village, there lived a family with a power that cannot be shown to the world. They lived while protecting and passing down the family heirloom, the "Key of Egg". However, some decades ago, it was stolen away, and they now live lives devoid of meaning. The protagonist Selafina is treated as a princess in this village. But one day, a letter arrives addressed to Selafina from Anju, a girl that disagreed with the family hiding away in a village, and escaped. "I found the Key of Egg. Let's have a competition, and see which one of us can return with it in hand. If I win, I shall become the true princess of the village. If they do not accept me as such, the Key of Egg shall not be returned." Upon reading this, the village elders, unable to let a chance to recover the Key of Egg slip away, send Selafina to Anju as requested. It seems the Key of Egg is to be sold at a large auction house in the trading city of Mirado. In this big city, what will happen to Selafina...?