The protagonist, Ryu, has finally reached the 100th floor of the dungeon, a feat she never imagined possible given her childhood struggles against even weak monsters. After her village was destroyed, she wandered aimlessly until finding herself at the entrance of this cave. Now, at the deepest level, she confronts the final boss.
Upon descending, Ryu encounters an old man with a white beard who reveals himself to be Vandalsia, the King of Destruction. He transforms into a monstrous form, explaining his past reign of terror and his desire for revenge against the heroes who sealed him away. Vandalsia attacks Ryu with "Catastrophe," a devastating spell that creates and detonates spheres of destruction. Ryu narrowly dodges, sustaining a significant injury to her shoulder. Despite the overwhelming power of the King of Destruction, Ryu fights back with her "Sonic Ripper" and a desperate, close-quarters assault, eventually defeating him with her powerful sword.
After her victory, Ryu is overwhelmed with emotion, realizing she has conquered her first dungeon. She recalls a fond memory of her childhood friend, Klinka, and the peaceful days before her village was burned down by monstrous creatures and a one-winged demon. This traumatic event led to her parents' deaths and her subsequent solitary journey.
Emerging from the dungeon, Ryu finds the outside world to be surprisingly easy to navigate, easily defeating a Hell Bear. She heads towards a town, intending to visit her village and seek information about the one-winged demon. Upon arriving in the bustling town, Ryu struggles to interact with people due to her prolonged isolation and inability to read or write. She is helped by a kind girl named Roel, who assists her in registering with the Adventurer's Guild. During this process, Ryu learns that her village was destroyed over ten years ago, meaning she spent a decade in the dungeon.
Roel, a low-level healer, offers Ryu a place to stay and proposes they form an adventurer party. Ryu, grateful for Roel's kindness and recognizing her own lack of knowledge about the outside world, accepts. They learn that reaching higher adventurer ranks, like A-rank, is necessary to enter the area around her former village, which is now sealed off due to dangerous monsters.
Their first mission together is to retrieve water from the Avangard Cave. Inside, they encounter weak monsters, but Roel struggles with panic and anxiety. Ryu, despite her own solitary fighting style, tries to support Roel, encouraging her to practice her healing magic. They also encounter a powerful "Greedy Great Cobra," which Ryu swiftly defeats, protecting Roel. Roel, though still timid, begins to show signs of growth.
Later, Ryu and Roel join a mission to hunt a Poison Salamander. The mission is led by the A-rank warrior Gantetsu and B-rank priest Etram. During the fight, Ryu secretly lands the finishing blow on the Poison Salamander, but Gantetsu takes credit. This leads to a confrontation where Ryu, fueled by her past trauma and Gantetsu's dishonesty, accuses him of stealing her achievement. Gantetsu, after a moment of silence, explains the importance of lower-rank missions and learning from them, urging Ryu to understand the value of helping others regardless of the reward. He also hints that the Poison Salamander's aggression might have been provoked by someone entering Bear's Forest.
Following this, Ryu and Roel continue their adventures, taking on various quests. They discover that Ryu's level is so high it causes the level-measuring machines to malfunction. They also learn that the one-winged demon that attacked Ryu's village is a mystery, with little information available. Ryu begins to understand the importance of teamwork and helping others, not just focusing on personal strength and rank.
