Spider Riders: Oracle no Yuusha-tachi  

Spider Riders, Spider Riders: The Heroes of Oracle, スパイダーライダーズ ~オラクルの勇者たち~, スパイダーライダーズ ～オラクルの勇者たち～

There exists an unknown underground world beneath our Earth, known as the Inner World. This realm is home to brave warriors who battle with large spiders and are called "Spider Riders." According to his grandfather's diary, a young boy named Hunter Steel is traveling around the world. One day, while exploring a pyramid, he accidentally enters the Inner World. There, the ongoing war between the insect squad seeking control of the Inner World and Spider Riders continues. Oracle, the fairy queen of the Inner World, summons Hunter because she believes he will be the savior of her realm. However, Oracle's powers are sealed by Mantid, the ruler of the insects. To restore peace to the Inner World, Hunter must find and retrieve the four keys that hold Oracle's power. He enlists Spider Shadow, a giant spider chosen by Oracle, as a member of the Spider Riders to fight against their enemies.