Known for her semblance to the Sadako character of The Ring series, Sawako Kuronuma is given the nickname "Sadako" and misunderstood to be frightening and malicious like her fictional counterpart, despite having a timid and sweet nature. Longing to make friends and live a normal life, Sawako is naturally drawn to the cheerful and friendly Shouta Kazehaya, the most popular boy in her class. From their first meeting, Sawako has admired Kazehaya's ability to be the center of attention and aspires to be like him. When Kazehaya organizes a test of courage for the entire class and encourages her to attend, Sawako sees this as an opportunity to get along with her classmates, starting with Ayane Yano and Chizuru Yoshida. Through each new encounter and emotion she experiences, Sawako believes that meeting Kazehaya has changed her for the better. Little does Sawako know, her presence has also changed Kazehaya.

For more than 30 years, Dariel has been a loyal soldier in the Demon King's army, having been raised by Granverza, one of the Four Heavenly Generals. However, as Dariel lacks any magical potential, he is nothing but a disgrace in the eyes of Granverza's son, Bashubaza, who fires Dariel right after assuming his father's position as a general. Stripped of a home and a job, Dariel wanders the forests, where he stumbles upon a human girl named Marika running from a monster. After Dariel intervenes to help Marika, she invites him to stay at her village in return. There, he discovers that the reason he has zero suitability for magic as a demon is that he is, in fact, a human. However, Dariel is no ordinary human. Possessing potential that far outweighs even heroes, Dariel may soon find himself involved in the humans and demons' seemingly never-ending conflict, facing against the race he once considered allies.

High above the realm of man, the gods of the world have convened to decide on a single matter: the continued existence of mankind. Under the head of Zeus, the deities of Ancient Greece, Norse mythology, and Hinduism, among others, call assembly every one thousand years to decide the fate of humanity. Because of their unrelenting abuse toward each other and the planet, this time the gods vote unanimously in favor of ending the human race. But before the mandate passes, Brunhild, one of the 13 demigod Valkyries, puts forth an alternate proposal: rather than anticlimactically annihilating mankind, why not give them a fighting chance and enact Ragnarök, a one-on-one showdown between man and god? Spurred on by the audacity of the challenge, the divine council quickly accepts, fully confident that this contest will display the utter might of the gods. To stand a chance against the mighty heavens, Brunhild will need to assemble history's greatest individuals, otherwise the death knell will surely be sounded for mankind.

Touya Mochizuki grows accustomed to his new life in another world. Armed with his trusty smartphone, the teenager accepts small quests at his leisure while spending time with his new fiancées: Yumina Urnea Belfast, Yae Kokonoe, and twin sisters Linse and Elze Shileska. But even in a relaxing environment, Touya is only beginning to understand the responsibilities that come with these engagements. In addition to his romantic woes, the elder fairy Lean wishes to locate the remaining pieces of Babylon, the floating island that the mysterious Professor Regina Babylon created five thousand years ago. Touya reluctantly accepts her request and seeks out the teleportation circles that will lead to the islands. However, strange monsters have emerged—possibly powerful enough to destroy the world. In order to save the second life he was given, Touya must weaponize ancient technologies to fight these monsters—all while balancing his overwhelming number of relationships.