The story begins with the protagonist, a hero named Alex, receiving his mission from the King to defeat the Demon Lord. After eighteen years of training, Alex is finally ready to embark on his adventure. The King introduces his party members: Rock, a red-haired warrior; Leon, a haughty mage; and Shirley, an enthusiastic priestess. To Alex's surprise, the King also introduces Hayashi, a man from another world who is described as an "salesperson." Hayashi presents Alex with a strange card bearing unfamiliar symbols. Alex is bewildered by Hayashi's profession and his seemingly ordinary skills, such as "Information Security Management Professional" and "IT Passport," which he doesn't understand. Despite Alex's protests that Hayashi is too weak, the King insists that Hayashi's otherworldly skills might be useful.
Upon reaching the first town, the party discovers that all accommodations are booked due to a harvest festival. However, Hayashi, accustomed to making travel arrangements, had already secured rooms, much to the relief of the party, especially Leon and Shirley who were eager for a bath. Hayashi explains he booked in advance after learning about the festival before leaving the capital. He also arranges for drinks and entertainment, ensuring the party enjoys a night of revelry.
The next day, Hayashi provides a relaxed sightseeing plan for the festival, allowing the party to recover from their hangovers and Shirley to indulge in shopping. Alex expresses his gratitude for Hayashi, acknowledging how much easier their journey has become thanks to him. Rock and Leon agree, recounting their own difficult past adventuring experiences, which highlight the value of Hayashi's logistical and organizational skills.
The party learns of a dragon residing in a nearby dungeon that possesses "Dragon Scales" capable of creating armor that can repel even the Demon Lord's magic. Alex decides they must acquire these scales. When Alex suggests Hayashi wait at the inn for safety, Hayashi refuses, stating he cannot abandon his "superiors" (the party) who are working overtime. The party, impressed by Hayashi's dedication and the comfort he provides, insists he accompany them.
Inside the dungeon, the party quickly gets lost. To their astonishment, Hayashi, who claims to be familiar with "stations" from his world, navigates them through the labyrinthine passages. They eventually reach the deepest chamber where they encounter a formidable Earth Dragon. While the party is overwhelmed by the dragon's pressure, Hayashi calmly introduces himself and offers the dragon alcohol as a gift. The dragon, pleased with the offering, becomes talkative and eventually sheds some scales for Hayashi, mistaking his plea for a "dragon's tooth" as a request for a souvenir to avoid being fired. The party is amazed by Hayashi's ability to de-escalate the situation and obtain the scales so easily.
Back in town, the party learns that the Dragon Scales cannot be fashioned into armor for Hayashi due to his low stats. The armor shop owner suggests an elf might be able to craft them. Hayashi, however, takes it upon himself to negotiate with other shops, securing a deal for the armor at a reduced price. He presents the shop owner with a contract and specifications, demonstrating his business acumen.
Later, while traveling to an elf village to have the armor crafted, the party encounters a large swarm of one-horned rabbits. Alex and Rock engage the rabbits, but a stray fireball from Leon causes friction between him and Alex. Hayashi intervenes, pointing out a movement that leads them to a single rabbit, which Leon captures. He also reveals the existence of a "storage bag" enchanted to preserve food.
During their journey, Alex and Leon have a heated exchange, which is overheard by Rock. Rock explains to them that in adventuring, there are no "givens" and that respect for each other's roles is crucial for a party's survival. He suggests that Alex and Leon's argument was orchestrated by Hayashi to give them a chance to reconcile.
Upon reaching the elf village, the party is met with incomprehensible ancient Elvish. Hayashi, using only body language, manages to communicate with the gatekeeper to find someone who speaks modern Elvish. He reveals he learned this skill during a two-year assignment in Myanmar where he couldn't speak the language. The party is touched by Hayashi's past experiences and his loneliness, reaffirming their commitment to him as a valuable member of their party.
The party then attempts to commission the elves to craft the Dragon Scales into armor. The elves initially refuse to help humans, but Hayashi offers them a box of popular sweets from the capital as a gift. When children snatch the sweets, the elf elder, impressed by Hayashi's thoughtfulness and the children's enjoyment, allows the party to enter the village.