YAMI NO NAKA NO CROWN

Yami no Naka no Crown summary:

Everyone in the world is born with two things: the ability to collect Life's Light and a Light Vessel in which to collect and hold it. Most people use their vessels to assist them in doing various tasks, but occasionally someone is born with a vessel that allows them to do battle. The protagonist, Ruyu, stumbles upon the end of a battle only to find one survivor. Could the young boy she saved be connected to the king's men who entered the town with the intent of killing everyone?

Everyone in the world is born with two things: the ability to collect Life's Light and a Light Vessel in which to collect and hold it. Most people use their vessels to assist them in doing various tasks, but occasionally someone is born with a vessel