Everything is built from glass in a world crafted from fire and sand. In the land of humans, civil war rages on. Kingdoms have fallen after the slave rebellion. To escape annihilation, they united under one and built the Crystal Kingdom. Then, they built a crystal castle on the back of a giant swallow, hid their queen inside, and sent her to the sky so no one could harm her. The slaves united and created the House of the People.The Miners and the Glaziers, the two main parties, have their own internal rivalry. Peace has prevailed between the two camps, thanks to the wisdom of representatives from both sides.  With the help of royal defectors, the rebellion managed to create an elite group of fighters, the Skywalkers. They aim to find the swallow that travels relentlessly through the skies, kill the queen and end the war. Arsen is a Skywalker. Imprisoned for a decade now inside a crystal cage, he is waiting for the day to set them free. He doesn't care who is going to win the war anymore. He just wants revenge for his brother's murder.