The protagonist, Trao, a merchant adventurer, is unceremoniously kicked out of his party, Blue Ring, by their leader, Rainer. Rainer, along with the priest Ciel and the mage Louise, accuse Trao of being a liability due to his lack of combat ability and his frugal financial management, which they see as hindering their desire for new equipment. Ciel complains about wearing smelly, second-hand priest robes, while Louise is disgusted by her dragon-blood-stained, death-scented mage robe, which attracts ghouls. Trao defends his practices, arguing that buying used items is cost-effective and that their current gear will soon be obsolete as they level up.
The true reason for Trao's expulsion, however, is revealed to be his misuse of party funds. Rainer accuses him of using the money to support Garnet, an all-female party of adventurers several years their junior. Trao admits to financially supporting Garnet, explaining that as a merchant, he always seeks a return on investment, but his explanation is met with disgust from his former party members. Rainer declares Trao a traitor and demands he leave the party's funds behind.
Before departing, Trao warns Rainer that an immediate attack on the Demon Lord is premature and ill-advised, citing insufficient information and resources. Rainer dismisses his concerns, believing Trao's caution stems from his merchant's inability to comprehend true strength.
Trao then seeks out Garnet, led by the warrior Rio, with members Lilith (priest) and Dominique (mage). He reveals that he has been secretly funding and training them for four years, using them for reconnaissance and other less savory tasks to support Blue Ring's ultimate goal of defeating the Demon Lord. He explains that he was expelled because Blue Ring intends to join an S-rank party called Golden Fang in an assault on the Demon Lord's territory, a plan Trao believes is doomed to fail.
Trao proposes a new plan: Garnet will now be the primary party, and he will join them. Their immediate goals are to gather intelligence on Golden Fang's invasion route and to hoard essential supplies, which they will later sell at inflated prices. Trao justifies this by stating that as a merchant, he must seize opportunities to profit.
As Garnet follows the main invasion force, they witness the S-rank parties' battle with the demon general Bechel and his forces. The battle results in a complete annihilation of the invasion force. Trao, unfazed, instructs Garnet to scavenge the battlefield for weapons and armor from both the fallen adventurers and the demon soldiers. His former party members, Rainer, Ciel, and Louise, are among the deceased, and Trao unceremoniously loots their belongings, including Rainer's sword and ring, and Louise's robe.
Meanwhile, the Demon Lord Bastuza, having lost his trusted general Bechel, recalls his other four Heavenly Kings due to fears of internal rebellion and the suspicious disappearance of the battlefield equipment.
Trao and Garnet return to their base, where Trao reveals his plan to use the plundered goods as capital to start a business. He intends to mass-produce a potent, addictive potion that was previously created by Dominique. This potion, designed to enhance mental faculties and prevent status ailments, has a dangerous side effect of high dependency. Trao plans to sell this potion to monsters, initially for free to create demand, and then for exorbitant prices, using the spoils from occupied territories. He argues this will slow the demon invasion and ultimately benefit humanity.
Garnet's members are tasked with gathering ingredients, refining the potion, and managing distribution, all while operating in a decentralized manner to avoid detection. The potion's widespread distribution leads to a significant slowdown in the demon army's advance, as monsters become preoccupied with acquiring the potion and humans learn to appease them with gold.
Trao then embarks on a quest to acquire powerful artifacts. He travels to the island nation of Yamato, where he negotiates with the king to fund the renovation of the shrine of the god Kusanagi in exchange for half the profits from the improved tourist attraction. He also secures a divine sword for the warrior Rio and arranges for the construction of a museum dedicated to the goddess Aigis, in exchange for her shield. He then procures a large quantity of Orichalcum to have Kusanagi forge a hundred swords, and secures Aigis's blessing for Dominique.
Finally, Trao recruits a large number of adventurers for a final assault on the Demon Lord. He plans a selection process involving acquiring legendary armor from the lake maiden Nimue, using a trick involving the Black Lotus plant to manipulate her into exchanging armor. He then uses the acquired artifacts and the vast wealth he has accumulated to prepare for the ultimate confrontation.
