In an era when Samurai ruled Japan… The Shinsengumi has been wiped out by an unknown attacker, leaving one survivor. Seven criminals are chosen as doubles for the Shinsengumi. To protect the security of Kyoto, a top-secret replacement operation is executed.

In her house, Mei Onigami discovers a strange round creature that only says "chimi." Her sisters, Mutsumi and Hazuki, agree to let the being stay with them until its owner comes to claim it. However, as soon as one of them utters the word "hell," more creatures show up until there are 12 in total. The sisters think nothing of this until the critters create a portal that summons an envoy from Hell. Jabberwock the Eighth, a horned and fanged man covered in fur, has come to unleash a living hell on earth under orders from his boss. However, when living in the human realm proves to be challenging, the Onigami sisters allow him to stay with them. They also take in his "Chimimoryo spirits"—the round demons that preceded his arrival. Called Jigoku-san by the Onigami sisters, this messenger from Hell has a lot of work cut out for him if he wants to take over the world. But before that, he will have to survive the everyday hells of human life.

Tooru Kirishima's notoriety is spread far and wide in the underworld. He is most commonly known as "The Demon of Sakuragi"—a man who is not afraid to resort to violence if deemed necessary. After almost jeopardizing a peace treaty, his boss tasks him with the most difficult job he has ever had: taking care of seven-year-old Yaeka Sakuragi—the boss' precious daughter—so that Tooru understands what it means to be responsible for another life. At first, the two do not seem to meet eye to eye, as Tooru has no clue on how to communicate with Yaeka, and the young girl is not used to expressing her emotions. However, as time goes on, they come to understand each other despite their differences. The fearsome right-hand man of a yakuza boss and the child he must protect are about to learn that family is not always bound by blood.

One day, high school student Michio Kaga attempts to start a strange online game he found while browsing the internet. Instead, he gets transported to a rural village in the game's world, equipped with special skills and an overpowered sword. After collecting his thoughts, he finds himself battling against bandits and soon realizes that he cannot log out. Resigning himself to fate and accepting this reality, Michio sets out on a journey—enjoying his new life, conquering dungeons to earn money, and building a harem to satisfy all his manly desires.