"KING’S RAID: Successors of the Will" is a fantasy anime series adapted from the mobile RPG game "King's Raid." The story is set in the kingdom of Orvel, a land plagued by darkness and chaos caused by the resurgence of ancient demons. The narrative centers on Kasel, a young swordsman, and his companions as they embark on a journey to uncover the truth behind the demonic threat and protect their world.

Kasel, raised by the knight Kyle, inherits a sacred sword known as the Divine Blade, a weapon with the power to combat demons. Alongside his childhood friend Frey, a priestess, and the mysterious warrior Cleo, Kasel sets out to confront the growing darkness. Their journey is driven by the need to locate Kasel’s missing brother, Theo, who disappeared under mysterious circumstances. As they travel, the group encounters allies and adversaries, including Roi, a skilled assassin, and Clause, a loyal knight of Orvel.

The plot unfolds as the group uncovers the origins of the demonic invasion, tied to the ancient Demon King Angmund, who was sealed away centuries ago. The resurgence of demons is linked to the machinations of a shadowy organization seeking to revive Angmund. Kasel and his companions must gather the fragments of the Divine Blade, scattered across the land, to restore its full power and stand against the impending threat. Along the way, they face trials that test their resolve, uncover secrets about their own pasts, and confront the moral complexities of their mission.

The series explores themes of friendship, sacrifice, and the struggle between light and darkness. Key characters include Kasel, whose determination and growth as a leader form the emotional core of the story; Frey, whose healing abilities and unwavering support bolster the group; and Cleo, whose enigmatic past and combat skills add depth to the narrative. The antagonists, including the demon lords and their human collaborators, provide a persistent challenge, forcing the protagonists to evolve and adapt.

As the story progresses, the stakes escalate, culminating in a climactic confrontation with the forces of darkness. The series balances action, character development, and world-building, offering a cohesive narrative that ties into the broader lore of the "King's Raid" universe. The anime serves as an introduction to the game’s world while providing a self-contained story for viewers unfamiliar with the source material.