Ryoma Takebayashi is a young boy living by himself in a forest, who, in a previous lifetime, used to be a tortured middle-aged Japanese office worker. He meets a group of distressed travelers in the forest, and decides to save them.

Ryoma arrives at Miya's house, overflowing with trash from a nearby dump. Ryoma and his slimes show a remarkable ability to clean, a skill that, as it turns out, the town of Gimul desperately needs.

The laundry business is ready to open. Ryoma hires new employees to help get his business started, and throws a party to express his thanks to the friends who have supported him thus far.

Ryoma learns that people are targeting his shop because he has associated himself with the head of the Tamer Guild, Taylor. To combat this, Ryoma has new positive rumors spread about his shop and deals with any assailant who tries and attack him. Ryoma also learns that he's gained enough finances to open up a second shop in a different city.

Arriving in Lenaf, Ryoma doesn't waste any time and meets with Pioro, the head of the town Merchant Guild, and his daughter Miyabi. From there, Ryoma sets up his second shop with the help of his Slimes and later does a quest for the Adventurers Guild, where a Smash Boar confront him.

After a small incident in his store involving a couple of unruly customers, Ryoma decides to create reinforced glass in the mines. It's also there that Ryoma discovered the evolved form of a Poison Slime called the Medicine Slime. He would later also meet a new god that had taken a liking to him named Tekun.

Ryoma hunts a Smash Boar, and after he does, Callum arrives at Lenaf with Tony, Caulkin, Lobelia, and new hires to help open the second shop. Sometime after it opens, Ryoma returns to Gimul where he meets with Serge to talk about the Magical Item Market he plans on visiting.

Ryoma attends the Magical Item Market, where he meets Fedele, Dionme's grandson, and instantly bonds with him. He later develops some new deodorant pouches from the newly evolved Deodorant Slime and would soon become acquainted with G-Ranked adventurers Wist and Beck. Fernobelia would also meet with Ryoma for the first time too.

Elia's first month at the magical academy is uneventful, but she meets new friends, Michelle, Miyabi, Feila, and Kanan. After forming a group with them, they go on a two-day camping trip, which their individual skills manage to help out their student peers.

It's finally the day of the Founding Festival, and Ryoma's food stall is a hit with the people of Gimul. Once Ryoma has time for himself, he encounters a lost boy who he decides to take to the Guard Station. When the festival was over, Ryoma participated in one last performance held by the Semiroid Troupe.

Seeking to take on some adventurer quests from the Adventurer Guild to raise his rank, Ryoma accepts a delivery quest to someone in Keleban. The quest makes Ryoma gain a new acquaintance there and perhaps a future business opportunity.

A curious Ryoma learns about a certain upcoming festival through Eliaria's letter and decides to run a food stall at the festival.

Ryoma is introduced to the Semroid Troupe leader Prenance and, from him, learns about Tunnel Ants nesting in the Southern Fields outside of Gimul. Hence Ryoma decides to hunt the Tunnel Ants and, amid this, runs into Beck and his adventuring pals, which he later hires them as temporary staff to help with the upcoming Founder festival.

Following a request from Worgan, Ryoma and some of his fellow adventurer friends take on a quest in a nearby forest to harvest Treant materials. They get more than what they bargained for when they have to face off against an evolved version of the Treant monster, an Elder Treant.

After completing the quest to collect Treant wood from a nearby forest, Ryoma finds that the work for the upcoming Founders Festival is coming along nicely.

Ryoma and the Jamil family travel to Gimul, a mining town. There, Ryoma and Eliaria take the first steps in becoming professionals in their crafts. Ryoma is given another opportunity to flex his new powers.

Ryoma decides to strike out on his own as an adventurer and business owner. He discusses his plans with the ducal family, and works with Serge the merchant to put his business plans in motion.

The laundry business explodes in popularity, so Ryoma rushes out on day two to hire more help. He meets Fei and Li Ling, foreigners with a hidden past.

With the business going more smoothly than Ryoma ever imagined, Ryoma is able to go back to studying his slimes and adventuring. He discovers several new types of slimes.

Ryoma and Eliaria make another attempt to tame the limour birds. If they succeed, it would be a great milestone in their careers as monster tamers. However, whatever the outcome, their separation is inevitable as Eliaria leaves for school.

It turns out that the travelers Ryoma saved were the local duke and his family. Impressed by Ryoma's various skills and enamored by his personality, they offer to take Ryoma along on their journey.

Eliaria and Ryoma practice magic and combat in Gimul. They practice fighting against the weak but numerous monsters now infesting the abandoned mine shafts.

The Jamil ducal family are all experts in the art of monster taming magic. Ryoma and Eliaria receive the Jamil elders' tutelage to further hone their taming magic.

The Adventurer's Guild sets up a large-scale group of adventurers to deal with the massive monster infestation discovered in the abandoned mines. Ryoma joins them.