Kirito, the renowned swordsman of Sword Art Online, noticed something strange. His reflection in the mirror seemed younger, his face less lined, his black hair brighter. His body felt lighter, too, like he was shedding off years.

Initially, he dismissed it as an illusion caused by the game. But as days passed, his age regression became more evident. His skill level started to drop, affecting his battle performance.

The once undefeatable Kirito was now struggling with basic monsters. His friends and guild members started to worry. Something was definitely wrong.

Asuna, his trusted partner, was the first to voice her concerns. "Kirito, your level is dropping rapidly. You need to find out what's happening."

Kirito agreed. He decided to visit Cardinal, the system's AI, hoping to find a solution.

Once there, Cardinal explained that a rare glitch was causing Kirito's age regression and level drop. "It's an anomaly in the system," she said.

"Is there a way to fix it?" Kirito asked, his voice filled with desperation.

"It's not that simple," Cardinal replied. "The glitch is tied to your character data. It's like your digital DNA."

Kirito felt a cold chill running down his spine. "So, you're saying there's no way to reverse this?"

"There might be one," Cardinal said, "But it's risky. You would need to enter the deepest layer of the system, where the glitch originated."

Despite the risks, Kirito agreed to undertake the dangerous quest. He knew that this could be his only chance to return to normal.

Asuna insisted on accompanying him. "We're partners, Kirito," she said. "I won't let you face this alone."

And so, they began their perilous journey into the digital abyss, with every step taking them further into the unknown.

They battled monsters and overcame challenges, their bond strengthening with each trial. Despite his weakened state, Kirito fought valiantly, driven by his desire to return to normal.

As they delved deeper, Kirito's regression accelerated. He was visibly younger now, his sword heavier in his small hands. He struggled to keep up, but refused to give up.

Finally, they reached the core of the system. It was a swirling vortex of code, the birthplace of the glitch.

"This is it," Kirito said, looking at the vortex. "We need to get to the center and eliminate the glitch."

As they stepped into the vortex, a wave of energy hit them. It felt as if they were being pulled apart and put together again.

They fought against the disorienting sensation, pushing towards the center. It was a battle against time and their own bodies.

Finally, they reached the glitch. It was a pulsating mass of corrupted code. Kirito raised his sword and struck it, pouring all his remaining strength into the blow.

The glitch exploded in a burst of light, and everything went white. Then, everything returned to normal, the vortex disappearing.

Kirito and Asuna found themselves back in Cardinal's chamber. "You did it," Cardinal said, smiling. "The glitch is gone."

Kirito looked at his hands. They were back to their normal size. He felt the weight of his years return, his strength restored. He had succeeded.

Asuna hugged him tightly. "I'm so proud of you, Kirito," she said, tears in her eyes. "You did it. You're back."

Kirito smiled, feeling a sense of relief wash over him. He was back to his old self, ready to face new challenges. His age regression was over, and he was ready to level up again.