He woke up with a jolt. His veins felt like they were aflame, his skin a pale, sickly color. This wasn’t his world. It wasn’t his body. He was Muzan Kibutsuji, the king of demons from his favorite anime series, Demon Slayer.

He lumbered to his feet, taking in his surroundings. He was in a dark, ancient-looking cave, the same place where Muzan was shown in the anime series. A sense of dread trickled through him, but it was dwarfed by the strange sense of excitement buzzing under his skin.

He knew Muzan’s story. The first demon in history who could create more like him, with a single scratch. Muzan was not immortal though, he needed human blood to survive and the sunlight was his ultimate enemy. The former human recalled a plotline he could use to his advantage.

In the Demon Slayer universe, there was a rare flower called the Blue Spider Lily, which could turn demons immortal by making them immune to sunlight. But the flower was virtually nonexistent. He decided to set out and find it, using his knowledge of the anime and his newfound demon abilities.

It was night outside, perfect for him to travel. He leaped onto the rooftops, moving stealthily to avoid drawing attention. He didn’t want to risk an encounter with a Demon Slayer. His destination was a remote mountainous region, where the Blue Spider Lily was rumored to grow.

Subduing his inner turmoil, he focused on honing his demon abilities. Enhanced senses, fluid movements, and immense strength. Days turned into weeks as he pushed himself to the brim, determined to be prepared for whatever was coming.

His journey wasn’t uneventful. He had close calls with Demon Slayers, encounters with other demons, and numerous challenges. But his knowledge of the anime helped him navigate it all, slowly chiseling him into the ultimate predator.

Finally, he reached the rumored site - a luminescent blue flower nestled amidst the crimson leaves. Joy surged through him, but he quickly suppressed it. He needed to concoct the elixir with the flower. For that, he devised a plan.

He had to kidnap a human who knew of apothecary. A risky move, but he was left with no choice. He knew of a renowned apothecary in the nearby village and decided to abduct him under the veil of night.

Using his demon abilities, he managed to kidnap the man with minimal fuss. He ensured he was unharmed and made him understand that cooperating would be in his best interest. Muzan then revealed the Blue Spider Lily and asked him to concoct an elixir.

Following a few strenuous days, the elixir was ready. The man drank the elixir and felt an immediate burst of energy. He could feel his cells changing, adapting, becoming stronger. The wait to test the effects of the elixir was agonizing.

As dawn approached, he prepared himself. His heart was a frantic drum in his chest. The first rays of sunlight touched his skin, he held his breath. To his relief, there was no pain, no burning. He was immune to the sun.

After achieving his goal, he released the apothecary, warning him never to speak of this incident. Then he disappeared, leaving no trace behind. Now, he could live as an immortal demon, unstoppable by any force.

However, he yearned to retain his humanity. Despite possessing a demon’s body, within he was still a human. He vowed to not harm humans and live in solitude, far away from the civilization.

He retreated deep into the mountains, living a life of solitude. Time seemed to halt for him as he found solace in his newfound immortality. He would watch the world pass by, an observer untouched by the sands of time.

His life was monotonous. But it was a small price to pay for his longed-for immortality. He spent his days observing humans from afar. He never interfered. He never approached them. He had become an observer, a non-participant.

But he remained ever vigilant. Although he was immortal, he was still a demon. The threat of Demon Slayers was always looming. He knew he was stronger but he also knew he couldn't underestimate them.

He occasionally ran into other demons, mostly hostile. He did his best to avoid confrontations but ended up having to defend himself. He realized being an immortal demon was a lonely and dangerous path, but he had chosen it willingly.

The former human's life was a series of lonely days and dangerous nights. But the tranquility of day and the thrill of night gave him a sense of fulfillment. He had chosen this path and he was content with it.

His lived his life, always on guard, always alone. And he was content. He had become truly immortal. It was a fragile balance, full of risks and sacrifices, but he found the beauty in it. He lived as an immortal demon, as Muzan Kibutsuji.

Years turned into decades, and decades into centuries. The world changed, but he remained constant. He was a silent observer, witnessing the ebb and flow of humanity. He found joy in the small things, satisfaction in his solitude.

He learned to exist harmoniously with the world. He never interrupted the natural order, never revealed his true nature. He watched the story of humanity unfold from the sidelines, the ultimate spectator, the immortal demon.

Over time, he learned to appreciate his solitary existence. It was a lonely path, but it brought him peace. He was content. He was an observer, a silent participant in the world's narrative.

His existence was a dance of shadows and light, of life and death. He lived eternally, a silent observer in the grand theatre of life. He was an immortal demon, unscathed by time and oblivion, ever-watchful, ever vigilant.

He was Muzan Kibutsuji, the king of demons, the silent observer, the eternal wanderer. He found his peace in his solitude, his satisfaction in his observation. He was truly immortal, immune to the sun, untouched by time.