The Demon King's Rebirth From Serenityium Element

Cid Gandesblood, a brave teenager with a thirst for truth, is obsessed with unravelling the mystery of his grandfather's disappearance at his mansion. In the midst of his investigation, an ancient book surrounded by a mysterious red aura, the elemental atoms of Serenityium, catches his attention. Instantly, Cid is sucked into a vortex of energy and stranded in Serene Australis, an alien galaxy full of wonders and dangers.

On this new world, Cid finds himself caught in a cosmic battle between 17 Demon Kings and 17 Angels who rule 17 different worlds.
Driven by a determination to find his grandfather and uncover the secrets of a mysterious book, Cid unexpectedly becomes the new Demon King. He must face tough challenges, master unexpected new powers, and fight against the forces of evil.

Cid's adventure in Serene Australis is an epic battle of self-discovery, uncovering the truth about his grandfather and family.