Despite being a handyman with a wide range of skills, Saitou is severely undervalued and underpaid. When he complains, his boss fires him, claiming that he is easily replaceable. As if his luck was not bad enough, Saitou soon finds himself about to be run over by a truck on his way home. Surprisingly enough, Saitou does not die; instead, he is transported to another world. There, he meets a party composed of the female knight Raelza, the moonlight fairy Lafanpan, and the mage Morlock, who are all coincidentally looking to recruit a new member with a skill set like Saitou's. Throughout their time together, Saitou uses his expertise to assist his fellow party members and soon comes to receive the recognition he never thought was possible. However, Saitou's presence may just be the catalyst that will connect a diverse cast of people from different places, slowly uncovering the fate that could bring a great change to this world.

Eight hundred years ago, terrifying demons threatened mankind's existence. On the brink of extinction, humans prayed to their gods, calling out for someone to save them. Emerging from these desperate pleas for salvation, battle deities known as the "Idaten" were born. Possessing unnatural strength and endurance, the Idaten managed to defeat the demons and an era of unprecedented peace was finally ushered in. Having never encountered demons before, the present generation of Idaten knows nothing of the demon's brutality, but they have instead only lived a peaceful existence. Training under Rin, the only remaining Idaten from 800 years ago, the new Idaten find ways to survive in a time where they have seemingly outlived their usefulness. However, when the tyrannical Zoble Empire resurrects a demon, the misfit crop of gods are called to the battlefield against their natural enemy once more.

After the mysterious mana calamity, Rudeus Greyrat and his fierce student Eris Boreas Greyrat are teleported to the Demon Continent. There, they team up with their newfound companion Ruijerd Supardia—the former leader of the Superd's Warrior group—to form "Dead End," a successful adventurer party. Making a name for themselves, the trio journeys across the continent to make their way back home to Fittoa. Following the advice he received from the faceless god Hitogami, Rudeus saves Kishirika Kishirisu, the Great Emperor of the Demon World, who rewards him by granting him a strange power. Now, as Rudeus masters the powerful ability that offers a number of new opportunities, it might prove to be more than what he bargained for when unexpected dangers threaten to hinder their travels.

In the immediate aftermath of the mana calamity, Sylphiette finds herself teleported to the heart of the Asura Kingdom: the royal palace. Her sudden appearance accidentally saves the life of second princess Ariel Anemoi Asura, who has her sights set on becoming the ruler of the realm. Witnessing Sylphiette's talent with combat magic firsthand, Ariel recruits her as her bodyguard and right-hand woman, commencing their journey to power—which proves far more treacherous than first imagined.