Humans are at war with a vicious being/race called the Dalki. Some humans, who have hidden for generations and possess special abilities, decide to help the rest of humanity, while others keep their powers secret.

The main character, Quinn, has lost his home and family due to this war. The only inheritance he has is an old book he can’t even open — until one day it unlocks and grants him a “system” (a game-like mechanism that gives quests, powers, etc.). Quinn uses the system to complete tasks/quests and gains strength. But things get complicated when the system gives him a quest: “It is time to feed!” He must drink human blood within 24 hours, or his HP will keep dropping until he completes the task.