Prolog

Ten years ago, the world underwent an unexpected change when the mysterious Reincarnation Tower appeared. Everyone could see this tower from any corner of the world; it did not exist in the physical realm of Earth but in another dimension. Each individual who turned 15 found a mark of the Reincarnation Tower on their right arm, along with deep information about the tower suddenly appearing in their minds. This mark was not merely a symbol; it indicated access to a new world, a portal to dungeons filled with power and opportunity.

The dungeon world promised by the Reincarnation Tower offered enticing rewards: incredible strength, longevity, and the ability to acquire anything one desired.

Additionally, the Reincarnation Tower warned that within a year, the Earth would mutate, and various creatures would evolve. If humanity wanted to survive, there was no choice but to seek power from the Reincarnation Tower. Because of these threats and the alluring offers, many rushed to enter the Reincarnation Tower.

However, being pioneers, there were many unknowns, and numerous dungeons remained unexplored, leading to only one in ten survivors. Yet, every survivor returned with extraordinary power, causing many to chase after strength and authority without hesitation, despite the high death toll.

As time passed, adventurers began to understand the intricacies of the dungeons. The initially high death rate started to decline, and an increasing number of individuals with superhuman abilities emerged. However, the rise of this power brought unexpected consequences. With newfound strength, many felt no need to adhere to existing norms and laws. Within six months of the tower's emergence, crime rates skyrocketed worldwide. The previously orderly society began to fracture, and instability started to spread.

Amid this chaos, governments around the world struggled to maintain law and order. Their heavy weaponry, from machine guns to nuclear arms, still functioned as effective deterrents, preventing a complete collapse of order. Yet, the shadow of threat loomed ever larger, and tension rose as time passed. Everyone knew that the one-year deadline was approaching, and uncertainty about what would happen next filled the air.

On that fateful morning, exactly one year after the Reincarnation Tower's appearance, the world was shrouded in mysterious fog. This fog was not merely a natural phenomenon; it seemed to signal that something greater was approaching. In an instant, savage beasts that had previously hidden in the depths of the ocean and earth began to emerge, attacking nearby cities with terrifying force. This assault shook humanity's status as the rulers of the Earth, a position they had held since ancient times.

A long battle ensued. In an effort to maintain their power, humanity deployed all available weaponry, including nuclear arms.

The prolonged conflict raged on. After exhausting all their weapons, including nuclear ones, humanity eventually managed to retain their hold on the Earth. But now they faced a dilemma, as various materials used to manufacture weapons seemed to have vanished or transformed into other forms since the fog appeared.

The loss of weaponry meant that government dominance had diminished. Many ambitious individuals seized the opportunity, and various guilds began to emerge, taking over roles previously held by nations.

Ten years later, the world had changed drastically. The once-clear divisions between countries had vanished; cities and regions had been overtaken by guilds, consortiums, and powerful families.

A new era had begun, where competition, power, and ambition reigned supreme, and everyone struggled to find their place in a world that had forever changed.

.....

Sunlight filtered through the gap in the curtain, illuminating a small, simple room. A young girl, appearing to be 15 years old, woke up from her sleep, still feeling drowsy. She had short silver hair and black eyes. With a delicate appearance and a slender profile, standing at 170 cm tall, she had a beautiful face.

The girl quickly got up and began preparing breakfast for herself and her brother.

Knock... knock... knock...

"Sora... wake up, it's time for breakfast."

The girl gently knocked on the door and called out to her brother.

After a long silence with no response, she helplessly opened the door, knowing her brother had not yet woken up.

Entering the room, she saw a cute-designed space for a girl, adorned with various neatly arranged dolls.

On the bed lay a handsome boy, seemingly perfect like a doll, with long silver hair cascading over the bed. He wore somewhat disheveled pajamas, exposing pale, smooth shoulders to the air. His appearance was striking and delicate, making it hard for any girl who looked at him not to have impure thoughts.

"Sora, wake up," the boy said softly, shaking his sister's body gently.

Perhaps sensing the touch of another, the girl opened her eyes. Her gray eyes seemed to emit a captivating glow, momentarily stunning her brother. But he quickly remembered that she was his sister.

"Good morning, Haru," Sora greeted, rubbing her eyes.

Indeed, they were Kasugano Haru and Kasugano Sora, twin siblings from the anime "Yosuga no Sora."

"Wake up, Sora, I've prepared breakfast," Haru said gently.

"Just a moment," Sora replied before getting out of bed and walking toward the bathroom.

Not long after, the sound of splashing water could be heard from the bathroom.

.....

"Haru, tomorrow is your 15th birthday and that also means you will enter the unfolding tower" Sora suddenly said as they ate, her voice filled with concern.

"I know you're worried about me, but I have to go. The savings our parents left us are almost gone. I want you to live a better life," Haru replied softly.

"But..."

"Don't worry, I'll be careful. Besides, haven't I been preparing for this for years?" Haru interjected, showing off his body, which, though slim, seemed to possess an explosive power. Haru had undergone physical training for years, developing a proportionate and coordinated physique. When dressed, he looked slender and slim, but he was filled with well-coordinated muscles.

Even though Haru had reassured her, Sora still felt uneasy. Throughout their lives together, even though they lived simply, she had no complaints. But she was also grateful that Haru continuously thought about her.

.....

The dim moonlight filtered through Haru's bedroom window, creating soft patterns on the wooden floor. Tonight, Haru sat on the edge of his bed, waiting with a mix of hope and nervousness for the arrival of the reincarnation tower's mark. This whirlwind of emotions lingered in his mind, balancing between the excitement of starting a new life and the fear of what would happen next. Yet, above all, what mattered most to him was Sora. Sora would lead a sad life if the savings left by their parents ran out.

Haru had certainly thought about working, but the reality was that he did not meet the basic requirements needed. In this world, the prerequisite for being able to work was having entered the reincarnation tower at least once. When someone entered that tower, they would receive a basic physical enhancement that made their abilities surpass those of ordinary humans. That's why both of them could only rely on the savings left by their parents.

As midnight approached, with the clock's hands indicating 12 AM, Haru felt his heart race. His right arm suddenly emitted a faint silver light. In an instant, a mysterious tower-shaped mark appeared on his skin, glowing with an intensity that mesmerized him.

However, as the mark appeared, a mysterious power seemed to seep into him. A sharp pain struck his head, causing him to fall onto the bed. In a flash, new memories began to flow into his mind, as if filling the emptiness within. Haru felt as if time slowed down, and each fragment of memory that emerged felt real and precious.

After a moment, the pain subsided, and those memories organized themselves neatly in his mind. Haru wiped the cold sweat from his forehead, taking a deep breath to calm himself.

"So that's how it is..." he murmured softly, his voice almost inaudible. Now, he realized that this was his second life.

His previous life ended in a tragic traffic accident. However, he never expected to be reborn as Kasugano Haruka, a character from an anime he had watched in his previous life. The anime world he had once considered merely a fantasy turned out to be real, albeit with significant differences—the existence of the reincarnation tower changed everything.

Haru felt confused as to why his memories were sealed. Perhaps it was a consequence of crossing dimensions or something else he couldn't comprehend. However, he was determined not to dwell on it too deeply. He needed to focus on his new life and what awaited him at the end of the road.

From his memories as Haru, he knew that the dungeons within the reincarnation tower were the very anime world he had once watched in his previous life. Strangely, even though this world was Earth, none of the anime he recognized from his previous life existed here. He felt that if he could leverage his knowledge of the plot, he could gain maximum advantage in the dungeons. Of course, with the lesson that even the world of *Yosuga no Sora* had a reincarnation tower that made the plot collapse, he wouldn't take everything in anime at face value; he would use it as a reference.

Haru didn't care who he was in his previous life. What mattered most to him now was living his new life as Kasugano Haruka and taking good care of Sora. He wanted Sora to have a better life, a life worthy of her after losing her parents. With strong determination, Haru stared at the tower mark on his right arm.

"This is a new beginning," he thought. He focused his mind on entering the reincarnation tower. Along with the blinding silver light, Haru felt as if he were being pulled by an invisible force and vanished from his room. He didn't know what awaited him inside the tower, but he was ready to face any challenge for Sora.