Caliber is a 13-year-old who has bigger dreams than the life he currently lives with his adoptive family. He wants to become an explorer and escape his hometown, Kinallen, once and for all. However, there are hurdles he must overcome to reach his goals. Taking on his new role of assassin, he discovers his strength in hand-to-hand combat, but prefers to hide in the shadows and rely on stealth. Will he be able to complete an S Rank job at such a young age?