An apocalyptic event has ravaged Japan, leaving nothing but endless sandy plains behind, and a strange rusting disease terrorizes the remnants of civilization. According to the government, the horrific state of the new world is the result of mushroom spores being spread by the likes of Bisco Akaboshi, labeled the Man-Eating Mushroom. But Bisco would beg to differ. In reality, he is a Mushroom Protector, determined to uncover the legendary Sabikui mushroom—said to be the ultimate cure for the rusting disease. Joining him on his quest are his giant crab Akutagawa and the kind doctor Milo Nekoyanagi, who is actively searching for a rust poisoning treatment for his sick sister. Despite the prejudice aimed toward him by the common folk, Bisco refuses to give up on his quest to purify the rotting world.

Born into a new world after a life of stagnancy, Will awakens to the faces of a skeleton, a ghost, and a mummy. Living in the ruins of a city long fallen, the three raise Will as their own. The skeleton— Blood—teaches him to fight; the ghost—Gus—teaches him magic; and the mummy—Mary—teaches him religion and responsibility. Most importantly, they all teach him love. As Will grows up and learns about the world he was born into, he prepares for the day when he must finally set out on his own. For Will, this journey includes a lifelong promise. At their coming-of-age, every adult is required to swear an oath to the god of their choice, with the strength of the pledge affecting the degree of their sworn god's blessing. With his departure approaching, Will must prepare to accept the truth of his undead guardians and embark into a world that even they don't know the state of. Will discovers, however, that every oath must be fulfilled, one way or another.

Jr., the heir of Romana and his battle sabers Cherry and Lime, who have girl circuits are enjoying their peaceful life in Romana. Suddenly, the evil Star-Face and his sexadolls attack Romana in order to take over so Star-Face can become the next High Official. In order to truly become the next High Official and ruler of Romana, he must first eliminate Jr. This begins a battle for, not only Jr.'s life, but for all of Romana. (Source: ANN)

Second season of Saihate no Paladin.