The story picks up with the adventurer party "Aragure Ichimi" (Roughnecks) resting in an oasis-like area around a labyrinth spring on the 20th floor of the Tyros Labyrinth. They are frustrated and exhausted from their slow progress. The heavy warrior and the mage argue, with the warrior accusing the mage of wasting magic and the mage retorting that the warrior failed to protect the front lines. The other two party members, a light warrior and a scout, remain indifferent.
Their respite is interrupted by a young man named Row, a dungeon sherpa. Row, who appears to be in his early twenties with tied-back brown hair, arrives carrying baskets of herbs. He explains he was gathering medicinal herbs that can be sold for a decent profit. The Roughnecks' leader, the heavy warrior, is displeased that their sherpa is moonlighting, but hesitates to complain as Row's guidance had recently saved them from a dangerous situation. The light warrior questions if gathering herbs is part of a sherpa's job, to which Row clarifies that their contract was for the shortest route to the 30th floor and only the labyrinth spring, not for herb gathering.
Row then displays various colored potions: healing, fatigue recovery, morale boosting, and mana recovery. He explains that the Roughnecks, having depleted their resources, might be short on potions. The mage inquires about the prices, which are listed on a chart. Row reveals that prices increase with labyrinth depth, with mana potions costing ten silver coins on the 20th floor. The heavy warrior protests, calling it a rip-off, but Row explains market price fluctuations based on ingredient availability. Despite their complaints, the Roughnecks purchase several potions from Row, allowing them to continue their exploration. They reach the 25th floor but fail to reach their goal of the 30th. They return safely, with the party earning a meager profit of one gold coin after expenses. Row, however, makes a profit of one gold coin and two silver coins from his sherpa fees and potion sales. The heavy warrior vows never to hire Row again, but Row calmly offers his services for future labyrinth expeditions.
Back at the Sherpa Guild, Row reports to Gima, an elderly woman who praises his safe return. Row mentions encountering a "Demon Festival" and escaping to the labyrinth spring. Gima notes that Row is the third party to be dissatisfied with him, implying the Roughnecks are difficult clients. Row is told to go home and reassure his younger sister, Marine.
Row then encounters Gabor, a fellow sherpa who is struggling with his own difficult clients, the Roughnecks, whom he describes as "typical sherpa bullies." Gabor mentions that parties that get blacklisted by the Sherpa Guild become unable to hire guides, making labyrinth exploration nearly impossible. Row believes the Roughnecks will eventually move on to other labyrinths. Gabor then shares a rumor about the renowned adventurer party "Yoiyami no Tsurugi" (Sword of Twilight), the top-ranked adventurers in the kingdom, coming to conquer the Tyros Labyrinth. This party, led by a beautiful young woman, has cleared two labyrinths and reached the 78th floor of the Infinite Labyrinth in the capital. Row speculates that their goal might be to obtain the labyrinth core, which grants significant experience points and can level up an entire party.
Row visits his aunt Murau, to whom he entrusts his four-year-old sister, Mariete, while he is away. Murau is described as greedy and stern, and Mariete is shy, making their relationship difficult. Row apologizes to Mariete, promising to buy meat and milk for stew with his earnings. He reflects on the dangers of his profession and the difficulty of finding reliable childcare.
The next day, Row is summoned by the Guild Master, Gunji, a former ace sherpa. Gunji informs Row that "Yoiyami no Tsurugi" is coming to the Tyros Labyrinth and that the adventurer guild has directly requested a single sherpa for them. The requirements are strict: experienced and skilled, with adventurer level five or higher, and good interpersonal skills. Row is the only candidate who fits all criteria, as the other potential candidates, Viva and Zahn, are less personable. Gunji reveals that "Yoiyami no Tsurugi" intends to conquer the labyrinth solo, which is highly unusual and dangerous given their party level of twelve and the labyrinth's estimated deepest level of fifty-two or fifty-three, with an appropriate level of fifteen or higher.
Despite the immense risk, Gunji urges Row to accept the assignment. Gima, the former guild master, then appears with the leader of "Yoiyami no Tsurugi," a striking young woman named Yuika. Yuika confirms their solo approach to labyrinth conquest, emphasizing efficiency and speed over large groups. Row expresses concern about the high risk of total party annihilation, but Yuika counters that their proven track record and coordinated strategy mitigate this risk. Row, however, is hesitant due to his responsibility for Mariete.
Yuika then reveals that the guild has already submitted Row's recommendation, and Gima confirms it. Row, realizing he has little choice, agrees to the assignment after confirming the dive plan, compensation, and making arrangements for Mariete's care in case of his death. He also requests that Yuika call him by his given name, Row, and she agrees, calling him by hers.
The next morning, Row meets the "Yoiyami no Tsurugi" party: Yuika, the swift and aggressive light warrior Belly, the stoic scout Nook, and the eccentric sage Majikan. Belly is immediately hostile towards Row, suspecting him of taking advantage of Yuika, who had gotten drunk and stayed at Row's home. Yuika, however, defends Row, citing his helpfulness and the positive influence he has had on Mariete.
The party then proceeds to the Tyros Labyrinth's shortcut entrance. Row explains the labyrinth's history and the function of the shortcut. Inside, they establish a meeting point at a labyrinth spring on the 14th floor. Yuika declares their goal is to reach the 47th floor, and Row is tasked with guiding them via the shortest route. They discuss the types of monsters they might encounter, including a "Layer Master" called a Serpent Lion.
During their rapid ascent, Row's "Endurance Recovery" passive gift is revealed, impressing Yuika and the others. They encounter various monsters, including Apple Bees, which Belly efficiently defeats. Row's gift allows him to keep pace with the party's aggressive strategy, which involves rapid traversal and minimal engagement with lesser monsters. They also encounter a Serpent Lion, which Yuika subdues and adds to her collection of controlled monsters, along with Obsidian Wolves and other creatures, effectively creating a mobile army.
Their journey continues at an unprecedented pace, with Row's endurance and Yuika's monster-controlling abilities proving highly effective. They reach the 43rd floor, the current deepest known level, and take a break at a labyrinth spring. Row prepares a meal for the party, including his homemade smoked meat, which is highly praised. He also offers Yuika a special candy made from distilled Mind Potion, which, despite its unpleasant taste, helps alleviate mental fatigue. Yuika is touched by Row's kindness towards Mariete and expresses a desire to go on a picnic with them.
The party continues their exploration, reaching the 48th floor and discovering a new labyrinth spring. They also find a massive, unusual Cannon Vine formation. While the others are excited by the potential loot, Row notices subtle differences in the plant, suspecting it's not a standard Cannon Vine. Before he can fully warn them, Belly attacks, triggering a massive explosion of the Cannon Vine's pods.
The narrative then shifts to the party's continued exploration, focusing on their unique combat strategies and Row's role as a sherpa. Yuika's ability to control monsters, combined with her party's specialized skills and Row's support, allows them to progress rapidly through the labyrinth. They encounter various powerful monsters, including Lesser Demons and a Minotaur, and Yuika's strategy of using controlled monsters to fight other monsters proves highly effective. Row continues to provide logistical support, including preparing meals and managing monster core collection.
As they delve deeper, the party faces increasingly dangerous foes, including the labyrinth's guardian, the Tyros Dragon, which is rumored to be the strongest monster in the labyrinth. Row, despite his initial reluctance, becomes increasingly involved in the party's operations, even offering advice on monster weaknesses and strategies. The narrative highlights the party's exceptional synergy and their unconventional approach to labyrinth exploration, setting the stage for further challenges and discoveries.
