"Bikkuriman: Taiichiji Seima Taisen" is a fantasy anime series that revolves around a cosmic battle between two opposing factions: the Seima and the Jashin. The Seima, representing light and order, are tasked with protecting the universe from the Jashin, who embody chaos and destruction. The conflict is rooted in the struggle to control the "Bikkuriman," powerful beings who possess immense energy and influence over the balance of the universe.

The story begins with the introduction of Yamato Takeru, a young boy who becomes the central figure in the battle between the Seima and Jashin. Takeru is revealed to be the reincarnation of a legendary hero destined to wield the power of the Bikkuriman. As the narrative progresses, Takeru is joined by a group of allies, including other reincarnated heroes and Bikkuriman warriors, each with unique abilities and backgrounds. Together, they embark on a journey to gather the scattered Bikkuriman and prevent the Jashin from plunging the universe into eternal darkness.

The Jashin, led by the malevolent Emperor Zaggart, seek to harness the energy of the Bikkuriman to achieve their goal of universal domination. Zaggart commands a formidable army of dark warriors and monsters, creating constant threats for Takeru and his companions. The series features numerous battles, both on Earth and in other dimensions, as the Seima and Jashin clash over the fate of the universe.

Key characters include Takeru, whose growth and determination drive the narrative; Ryu, a skilled warrior and Takeru's loyal friend; and Princess Lila, a Seima leader who provides guidance and support. On the opposing side, Emperor Zaggart is a ruthless and calculating antagonist, while his generals, such as the cunning Dark Schneider, add complexity to the conflict.

The plot is structured around episodic encounters with various Bikkuriman, each of whom must be awakened or recruited to strengthen the Seima's forces. These encounters often involve moral dilemmas, tests of character, and revelations about the characters' past lives. The series also explores themes of destiny, friendship, and the struggle between good and evil, as Takeru and his allies strive to fulfill their roles in the cosmic battle.

As the story reaches its climax, the stakes escalate, with the Seima and Jashin engaging in a final, decisive confrontation. The outcome of this battle determines the future of the universe and the legacy of the Bikkuriman. The series concludes with a resolution that ties together the fates of the main characters and the overarching conflict, leaving a lasting impact on the world they fought to protect.