After being defeated in battle by the hero Gram in the magical world of Alneath in the year 1599, the immortal Demon Lord Veltol Velvet Velsvalt faced a long slumber. Five hundred years later, in 2099, his loyal subordinate Machina Soleige successfully performs the ritual to revive him, intending to restore him to power. However, during his absence, a catastrophic event known as the Fantasion occurred, causing the magical realm of Alneath to physically merge with the industrial world of Earth in the year 2023. This collision decimated ninety percent of the population, collapsed national borders, and led to wars that eventually forged a new reality of independent city-states.

The world Veltol awakens to is a vast cyberpunk metropolis where magic and engineering have fused into a new discipline called magineering, powering a dazzling but deeply unequal society. His destination is the city-state of Shinjuku, formerly part of Tokyo, a bustling hub of neon lights, skyscrapers, and advanced technology. Worse than the unfamiliar landscape is Veltol's crippling weakness. In this new era, his demonic power is no longer absolute; it is directly sustained by the fear, belief, and attention of his followers. With his legend reduced to a historical footnote and magic heavily regulated within city limits, Veltol is rendered nearly powerless, a relic in a world that has moved on without him.

To navigate this strange future, Veltol allies with Machina, one of his six surviving Dark Peers, and a spirited young hacker named Takahashi. Realizing that notoriety is the key to regaining his strength, they devise an unconventional plan for the ancient demon lord: he will become an online streamer. Veltol's arrogant and theatrical personality proves to be a hit, and he rapidly gains a massive following, converting their engagement into a tangible resurgence of his magical power.

The main antagonist quickly emerges as Marcus, another of Veltol's former Dark Peers who awakened earlier and adapted to the merged world. Instead of a dark fortress, Marcus now resides in a corporate high-rise as the CEO of Ishimaru Heavy Magical Industries, a powerful megacorporation that has created a device called the Familia. This device allows ordinary citizens to cast spells at the touch of a button, effectively democratizing magic while also controlling it. Marcus, who orchestrated the hunting and persecution of immortals to consolidate his power, views the resurrected Veltol as a threat to his dominance and dismisses him as obsolete.

The conflict escalates when Veltol and Takahashi uncover a horrific secret powering Shinjuku. The city's massive Aether Reactor, the source of its energy, does not run solely on aether; it also burns the souls of captured immortals as fuel, a scheme Marcus perpetuates to keep the city running. When Marcus kidnaps Machina to use her immortal soul as a temporary power source, Veltol is forced into a direct confrontation. Despite his weakened state, he uses the attention from a city-wide hacker broadcast to supercharge his abilities, allowing him to defeat Marcus and throw him into the very reactor he built.

Following this victory, the narrative shifts toward a more fantastical quest. Veltol sets out to locate the three remaining Dark Peers who disappeared after the worlds merged. To find the first clue, Veltol, Machina, and Takahashi enroll as students at a prestigious magical academy in a city controlled by Alneath's three great clans. Their goal is to infiltrate a sealed treasury that holds information on the missing lords. This arc involves navigating clan politics and confronting the goddess Meldia, a deity of luck and misfortune who fell in love with the hero Gram and granted him immortality, a gift that became a source of endless disillusionment for him. The overarching journey becomes one of an ancient tyrant adapting to a cyberpunk world, learning that true power in the Fused Era requires not just force, but followers, adaptability, and a grudging empathy for the people of his new domain.