Crest Bahurst, the fifth son of a duke in the kingdom of Rakind, has lived a miserable life. His mother died giving him birth, leading his father to resent him, his four older brothers to bully him, and even his childhood friend and fiancée, Ellis Refield, to treat him like a slave in an attempt to shatter his self-esteem. On his fifteenth birthday, during his coming-of-age ceremony, Crest receives a divine skill known as Gacha. However, under pressure from his father to demonstrate the skill immediately, Crest finds he cannot activate it as he lacks the necessary points. Humiliated and enraged, his father exiles him on the spot, and Crest is transported by guards to a magic circle that sends him to the Lower World, a dangerous forest teeming with monsters.

Armed with only a sword he convinced a guard to give him, Crest soon kills a wolf monster and discovers the secret to his power: he earns points by defeating monsters, which he can then use to activate his Gacha skill. Through this mechanic, the Gacha effectively functions as a universal cheat skill, allowing him to purchase and acquire a wide variety of other abilities. As he begins to methodically grind for points and grow stronger, Crest resolves to survive, get back on his feet, and eventually have his revenge. His goal is to achieve an easy, powerful slow life.

Back in the royal capital, the kingdom receives an urgent letter from the Pope, who has foreseen a massive monster attack. The prophecy names three specific skills as essential for combating this threat: Ellis s Blessing of the Saint, Minue Mycelian s Strike of the Hero, and Crest s Gacha. The king learns to his dismay that Crest has been banished. While Crest is a student, Minue, a fellow student in the knighthood department who knows of the abuse Crest suffered, volunteers to retrieve him. Ellis insists on going as his fiancée. After a tense dispute, the two grudgingly agree to journey together to the Lower World to bring Crest back before the monster horde arrives.