The protagonist, Yamada Tetsuya, a 23-year-old office worker who loves sleeping, buys a king-sized bed as a birthday treat. He wakes up not in his bed, but in a forest, with his bed floating beside him. Initially believing it to be a lucid dream, he discovers he can control the bed and fly. His dream takes a turn when he encounters a dragon attacking a young girl, Aria Astley, a 14-year-old adventurer burdened by her deceased parents' debt.
Driven by a sense of chivalry, Tetsuya intervenes, and to his surprise, his actions trigger a game-like system. He levels up rapidly, gaining powerful skills like "Flare Phalanx" and "Time-Space Severing Sword," which he uses to effortlessly defeat the dragon with a single punch. He learns that Aria's quest to defeat the dragon is invalidated because she didn't deliver the finishing blow, leaving her debt unresolved. Tetsuya, having learned "Resurrection Magic," revives the dragon, allowing Aria to defeat it and complete her quest, securing the reward money.
Aria, deeply impressed and grateful, accompanies Tetsuya, who is still in his pajamas and has no idea where he is. He summons his floating bed, and they travel to the town of Balevia. Tetsuya, impressed by Aria's kindness and determination, decides to register as an adventurer himself, gaining a "Dragon Slayer" title and further leveling up. He learns that Aria's debt is substantial and that the moneylender is exploitative. Tetsuya intervenes again, using his newfound skills to intimidate the moneylender into returning half of Aria's payment.
They then proceed to Aria's modest apartment, where Tetsuya's bed materializes. Despite his initial laziness and desire to stay in bed, Aria encourages him to move, though she also indulges his preference for rest. She reveals her motivation to become stronger to protect herself and others, asking Tetsuya to be her master. He deflects, claiming his rapid leveling is due to simple walking, a statement Aria finds unbelievable but eventually accepts as a lesson in perseverance.
The next day, Tetsuya and Aria accept a low-paying quest to defeat goblins for a beastkin village. They travel by bed to the village, where they meet the elder and a young fox-eared girl named Mimilii, who is surprisingly strong for her appearance. Mimilii, despite being only 15, is the strongest in the village and insists on joining the goblin hunt, much to Aria's initial dismay due to her own level. Tetsuya, however, discovers Mimilii's stats are comparable to Aria's.
While waiting for the goblins, Tetsuya and Aria are captivated by Mimilii's cuteness and are allowed to pet her ears and tail as a reward for their efforts. Mimilii reveals her parents are missing adventurers and that she is the village's strongest. As the goblins approach, the focus shifts to the impending battle.