Ayumu Narumi has lived all his life in the shadow of his famous detective brother, Kiyotaka. However, Kiyotaka disappeared two years ago, leaving behind his wife Madoka and Ayumu himself, along with a cryptic message about the Blade Children. One day, a girl at Ayumu's school suddenly dies. What seemed like a suicide at first glance turns out to be a murder, and Ayumu is the prime suspect. While investigating the person responsible for framing him, he discovers that the mysterious Blade Children are involved—and they somehow know Kiyotaka personally. Ayumu soon finds out just how dangerous the Blade Children are and learns that, in reality, he and Kiyotaka are intertwined more closely than he had ever believed.

Underneath the surface of the Earth lies the Inner World, a realm where a war rages on between intelligent spiders and the invading humanoid insects known as Insectors. However, the spiders are not alone, as Spider Riders—humans from the Outer World, known as Earthens in the Inner World, that are chosen by the Oracle—fight alongside them. Filled with wondrous tales of a mysterious pyramid and entrusted with his grandfather's journal, a young boy called Hunter Steele sets out on an exploration. There, his destined meeting with the Oracle occurs, and he is transported into the Inner World as a Spider Rider. Finding himself lost and confused in the middle of a forest, Hunter crosses paths with a giant spider named Shadow. Although reluctant, Shadow agrees to fight by his side. He then meets Corona—a skilled Spider Hunter and kind girl with a penchant for normal life. She shows him the ropes of being a Spider Rider, and educates him about the fate of the Inner World if the Insectors continue their tyrannical reign. Thus begins the story of Hunter Steele, a heedless young boy on a quest to save the Inner World. But his task of retrieving the four Oracle Keys holding the Oracle's true power will lead him to an ultimate clash against Mantid, leader of the Insectors.

The battle against the Insectors to save the Inner World rages on, as Hunter Steele and the Spider Riders defend Arachna. With the help of his friends—Igneous, an intelligent young royal officer of Arachna's military; Magma, a foolhardy warrior; and Corona, a kind-hearted girl—crisis has been averted—but not for long. News of the Kingdom of Nuuma being attacked by the Insectors is soon brought to the attention of the Spider Riders, who are reluctant to leave Arachna undefended. But past favors need to be repaid, so they decide to travel across the Inner Ocean to protect the Kingdom of Nuuma. Entrusted with finding four of the Oracle's keys locked away by the leader of the Insectors, Hunter and his friends strive to bring about peace once and for all. Spider Riders: Yomigaeru Taiyou is the epic conclusion to the Spider Riders series. Will the four Oracle Keys find their way to Hunter and the Spider Riders, or will Mantid and the Insectors finally have their wish granted, conquering the Inner World for themselves?

Corrupt politicians, frenzied nationalists, and other warmongering forces constantly jeopardize the thin veneer of peace between neighboring countries Ostania and Westalis. In spite of their plots, renowned spy and master of disguise Twilight fulfills dangerous missions one after another in the hope that no child will have to experience the horrors of war. In the bustling Ostanian city of Berlint, Twilight dons the alias of Loid Forger, an esteemed psychiatrist. However, his true intention is to gather intelligence on prominent politician Donovan Desmond, who only appears rarely in public at his sons' school: the prestigious Eden Academy. Enlisting the help of unmarried city hall clerk Yor Briar to act as his wife and adopting the curious six-year-old orphan Anya as his daughter, Loid enacts his master plan. He will enroll Anya in Eden Academy, where Loid hopes she will excel and give him the opportunity to meet Donovan without arousing suspicion. Unfortunately for Loid, even a man of his talents has trouble playing the figure of a loving father and husband. And just like Loid is hiding his true identity, Yor—who is an underground assassin known as Thorn Princess—and Anya—an esper who can read people's minds—have no plans to disclose their own secrets either. Although this picture-perfect family is founded on deception, the Forgers gradually come to understand that the love they share for one another trumps all else.