Yami no Naka no Crown

In this world, every person is born with the ability to gather "Life's Light" and a "Light Vessel" to store it. While most use their vessels for everyday tasks, some possess vessels that enable combat. Ruyu discovers the aftermath of a battle and finds a single survivor, a young boy. She rescues him, raising questions about his possible connection to the king's soldiers who arrived in the town intending to kill everyone.