In DxD Starting with Sign-Ing in as the Red Dragon

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If Kirei Kotomine and Tokiomi Tohsaka represented the most intense conflict in the Holy Grail War, then Rider and Waver, as well as Caster and his loyal disciple, Ryuunosuke Uryuu, were the most harmonious pairs.

"My King, Waver has not disappointed you," Waver said, his voice calm and steady despite his youthful appearance. This was the Waver of ten years later, matured and resolute.

Rider laughed heartily, slapping Waver on the back. "Hahaha! Loyalty from a subject to their king is the greatest wish of any ruler! Even if the odds are against us, we'll charge into battle together! Are you ready to fight by my side once more?"

"Yes! I will follow you to the ends of the earth!" Waver replied, his voice filled with determination.

For ten years, Waver had longed for this chance to make up for past regrets. Now, he was ready to fight alongside his king once more.

Meanwhile, Caster, Gilles de Rais, was overcome with emotion. Upon learning that his loyal disciple, Ryuunosuke Uryuu, had met a tragic end in the future timeline, he broke down in tears.

"Why? Why must such a devout and pure soul suffer such a cruel fate?!" Caster cried out, his voice filled with anguish. "The world is unjust!"

Suddenly, Caster sensed a powerful surge of magical energy in the city. It wasn't ordinary magic—it was ancient, divine magic, but used in a peculiar way.

Driven by curiosity, Caster rushed to the source of the magic. There, he found a man who radiated an otherworldly aura.

"Ah, you have the presence of a Servant. How fascinating," Caster said, his eyes gleaming with excitement. "Would you be willing to assist me in a little experiment?"

Half an hour later, in the river of Fuyuki City, a massive sea monster rose from the depths.

"My Jeanne! This time, I will make you remember your true name!" Caster declared, his voice filled with madness.

With his newfound power, Caster had summoned a monstrous abomination—a fusion of a sea demon and a dragon, its body covered in writhing tentacles and glowing with an eerie light.

Meanwhile, in another part of the city, Akira was enjoying a rare moment of peace.

"Akira-nii, do you know how sad I was when I realized I couldn't contact you through our contract anymore?" Illya said, her voice trembling as she clung to Akira.

"I thought about you every day, Akira-nii. I missed you so much," she continued, her crimson eyes filled with tears.

Like Sakura, Illya had been devastated by Akira's sudden disappearance. She had returned to the Einzbern family, determined to use the Holy Grail to bring him back.

During the Holy Grail War, Illya had reunited with Sakura and Rin Tohsaka. Together, they had formed an alliance, united by their shared goal of finding Akira.

"Akira-nii, now that we know the Holy Grail is corrupted, we have to save Mama!" Illya said, her voice filled with determination. "We'll force her to accept a chess piece and sever her connection to the Grail!"

Akira smiled, gently patting Illya's head. "We'll do it, Illya. I promise."

But before they could continue their conversation, a deafening roar echoed through the city.

Outside, the giant sea demon dragon had fully emerged, its massive form towering over the city.

Aoi Tohsaka, who had been resting in Akira's arms, stirred awake.

"What… what's happening?" she asked, her voice groggy.

Akira turned to her, his expression serious. "Aoi, do you remember the memories you saw earlier? The ones where you died?"

Aoi's eyes widened as the memories flooded back. "I… I died? And Tokiomi too?"

"Yes," Akira said, his voice calm but firm. "If I hadn't intervened, that would have been your fate."

Aoi's hands trembled as she processed the information. "But… you're still here. Does that mean you've changed the future?"

Akira nodded. "I've defied the world's will. The future is no longer set in stone."

Aoi's expression softened, and she leaned in to kiss Akira. "Then… I'll trust you to protect us."

As Akira prepared to face the giant sea demon dragon, he received an urgent message from the DxD world.

[Akira! Please, if you can hear me, come back!]

[Jeanne is using her life force to activate her Sacred Gear!]

It was Irina's voice, filled with desperation.

Akira hesitated for a moment. The sea demon dragon was a significant threat, but Jeanne and Irina were in immediate danger.

[Akira-sama, we need your help!]

[Xenovia and the others are in trouble!]

This time, it was Asia's voice.

Akira made his decision. "Asia, I'm allowing you to use your Balance Breaker. Hold off the enemy until I return."

With that, Akira activated his teleportation magic, leaving the sea demon dragon to Saber and the other Servants.

In the DxD world, Jeanne stood at the forefront of the battle, her Sacred Gear glowing with divine light.

"By the power of the Holy Sword, I summon thee—Durandal, the Tyrant's Blade!" Jeanne declared, her voice echoing with authority.

The blade materialized in her hands, radiating pure, destructive energy.

"Let's finish this!" Jeanne shouted, charging at the enemy with unwavering determination.

Back in Fuyuki City, the giant sea demon dragon roared, its massive form casting a shadow over the city.

Saber, Rin, and Sakura stood ready, their weapons drawn.

"We'll hold it off until Akira returns," Saber said, her voice steady.

The battle for Fuyuki City had reached its climax, and the fate of the world hung in the balance.

Note: So far this story is published up to chapter 90 on my patreon go take a look and remember if you reach 140 stones of power I will publish the next chapter.