The protagonist awakens in a stark white, featureless space with no memory of who he is. A disembodied voice instructs him to "give humanity a trial," stating that the power to do so lies within him and the reward will be his heart's desire. Confused and lacking any personal desires due to his amnesia, he is tasked with creating a dungeon to challenge humans.
His first step is to summon a familiar, a companion to aid in managing the dungeon. He chooses from a selection and meets a small, two-dimensional female figure with green hair and a camouflage uniform. She is initially rude, calling him "Don-game" (slow turtle), and reveals that all other potential familiars have already been chosen, leaving her as the last remaining option. Despite their rocky start and bickering, they eventually agree on names: the protagonist becomes Toru, and the familiar names herself Sena.
Sena reveals that Toru's role is to create dungeons, which are places filled with monsters and traps. Toru's first major challenge is selecting a location for his dungeon. Using a tablet-like device provided by Sena, he discovers that the only available location is the front of the Tokyo Metropolitan Police Department headquarters. This is a disastrous choice, as the police are trained to combat threats, and a dungeon appearing there would be immediately investigated and likely conquered, leading to Toru's demise.
Next, Toru must choose a class. The options are "Astrologer," which grants basic magic and precognition, and "Puppet Master," which allows for the manipulation of puppets. Despite the perilous location, Toru feels drawn to the "Puppet Master" class, even though it seems less practical for survival. He is forced into this choice when the "Astrologer" option disappears, implying another Dungeon Master has selected it.
With his class decided, Toru and Sena begin designing the dungeon using DP (Dungeon Points). They reject the "Initial Bonus Set" as too weak for their situation. Sena proposes a strategy of creating a minimal dungeon with a powerful boss monster, using the DP gained from defeating intruders to continuously strengthen the dungeon and revive summoned monsters. Toru, however, realizes this strategy plays into the hands of whoever orchestrated this situation. He devises an alternative plan: to create an "unbeatable beginner dungeon."
Meanwhile, two police officers, investigating a sudden sinkhole at the police headquarters, descend into the newly formed dungeon. They are guided by Sena, who explains the dungeon's purpose as a "tutorial." They encounter a puppet monster, which they defeat, learning about combat and drop items. Sena then demonstrates the harsh reality of the dungeon by killing them, only for them to revive, revealing that death within a beginner dungeon is not permanent, though the pain and fear remain. The officers are given wooden swords as rewards and are instructed to leave and report their findings.
The narrative then shifts back to Toru and Sena, who are still strategizing. Toru rejects Sena's initial plan, realizing that the goal is not just to defeat intruders but to create a dungeon that is impossible to conquer, thus defying the system that placed them there. He declares their intention to create an "unbeatable beginner dungeon." The chapter ends with the implication that Toru's defiance and unique approach will be the key to their survival and potentially challenging the established order.
