The story begins 15 years after the demon king was defeated and the world has become peaceful. Kotone, who graduated from school and became a magician, inquired about the kingdom-affiliated RPG Real Estate in order to find a new home. In reality, RPG Real Estate was Kotone's place of employment, and together with Fa, a demi-human, the priest Rufuria, and the soldier Rakira, they help support the searches of new homes for the customers with various circumstances.

As the most powerful entity of all time, the Demon Lord Varvatos thinks life is a big fat snore. When he takes matters into his own hands and decides to reincarnate, he calibrates his magical strength to be perfectly average. But there is no way he could have predicted that everyone in the modern world would be weak as hell, which means he is totally overpowered once again! Reborn under the name Ard, he has ladies fawning over him, the royal family begging him to become the next king, and an ex-minion insisting on killing him?! But Ard has a one-track mind, and he won't stop at anything to achieve his ultimate goal!

Yuuichi Katagiri has battled financial hardships his whole life but has learned to stay content and positive thanks to his close circle of friends. To keep a promise he made to them, Yuuichi saves up enough money to join them on the school trip. But when the gathered money mysteriously goes missing, suspicion falls on two of Yuuichi's friends: Shiho Sawaragi and Makoto Shibe, who were in charge of collecting the payments. Although innocent, Shiho and Makoto take responsibility for the failure to protect the money when no one else comes forward. A few days later, Yuuichi and his friends receive mysterious letters which trick each of them into meeting up. Upon arrival, they are ambushed and knocked unconscious. They wake up in a mysterious room in the presence of "Manabu-kun," a character from a controversial children's show that stopped airing due to its malicious content. He informs the group that one of them indirectly gathered them together in order to settle a large debt. They are to play a "friendship game": a series of games that will test the strength of their bond and trust in each other. As the group's faith wavers due to the growing number of secrets and betrayals, Yuuichi must figure out who of his "friends" he can actually trust and ultimately discover the identity of the traitor.

When Demon Queen Echidna begins her invasion of the human realm, the people turn to the hero Leo Demonheart to protect them. Blessed with insurmountable power, Leo easily repels Echidna's army, thereby saving the world. But instead of gratitude or admiration, Leo is met with disdain and scorn from his fellow humans, who fear his overwhelming strength and believe that it may eventually cause humanity's demise. Banished from the kingdom he once called home, Leo wanders aimlessly throughout the land until, one day, he hears rumors of Echidna's efforts to rebuild her army. Hoping that demonkind might accept him as an ally, he returns to the demon queen's castle and offers Echidna his help. Naturally, Echidna immediately rejects him. Still, not all hope is lost, as Leo manages to convince Echidna's four generals to let him secretly work under their supervision. Donning the identity of a masked dark knight named Onyx, Leo solves the demon army's problems one by one—gradually improving the quality of life around the castle. Above all else, however, Leo wants to accomplish one goal: to learn why Echidna started the war in the first place.