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

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As Akira rose into the air, a golden teleportation circle materialized on the ground below. From within the circle, Agumon's voice echoed. He had been preparing for this moment for some time.

"Akira doesn't have a suitable weapon right now. You have three holy swords—just toss one in here," Agumon demanded.

Without hesitation, Jeanne handed over the Excalibur she was holding. This particular holy sword wasn't hers to begin with; it had been created by Archer, making it the most suitable to give away. Soon, the holy sword was thrown into the golden circle, entering the mirrored space created by Agumon.

Akira's figure gradually materialized within the space. The moment he laid eyes on the sea demon, the system's notification rang in his ears:

[Ding!]

[Congratulations to the host for triggering a villain sign-in!]

[Sign-in Level: Gold.]

[Sign-in Type: Regional Sign-in.]

[Sign-in Location: The Necronomicon and the Golden Fleece.]

[Requirement: Simultaneously come into contact with the Necronomicon and the Golden Fleece.]

"Just as we thought, this monster is a new type of evil god," Akira muttered.

The massive sea demon had fused with the Golden Fleece, gaining additional demonic traits. Before being expelled, the World Will had introduced the influence of an outer god and attached a portion of its power to the sea demon, creating this abomination.

"Alaya… you really went all out, huh? You just discarded this world like it was nothing," Akira said, narrowing his eyes. "Well, if you don't want it, I'll take it for myself!"

[Boosted Gear!]

[Balance Breaker!]

[Cardinal Crimson Promotion!]

The crimson armor of the Boosted Gear Scale Mail instantly materialized, covering Akira's body. However, even with the Balance Breaker activated, Akira knew it wouldn't be enough to defeat this sea demon.

[Name: Outer God's Kin · World's Kin · Sea Demon (Genderless)]

[Level: 249 + 30]

[Note: It hasn't broken through to the Super Devil level yet, but due to the conflict between the Outer God's power and the World Will, its strength is unstable. Even so, it's a formidable foe.]

[Attribute Evaluation]

[Strength: B → B+]

[Speed: D → C+]

[Magic: C → C+]

[Durability: A → A+]

[Martial Arts/Skill Proficiency: C (Originally a fusion of chaotic forces, it had no martial arts or skill proficiency. However, after fusing with a portion of Alaya's power, it gained basic abilities.)]

[Sacred Gear/Bloodline Ability: S (The sea demon's innate power is at the peak of a high-class devil. Its attributes aren't particularly outstanding, but after fusing with the Golden Fleece, it gained demonic traits, significantly increasing its strength. Additionally, the Necronomicon summoned the mad will of an outer god, further enhancing its power and regenerative abilities. Finally, after merging with the World Will, its strength has reached an unprecedented level.)]

[Comprehensive Evaluation: Devil King Level (Although its rank hasn't reached that level, its combat strength has surpassed that of a Devil King!)]

[Note: A product of the fusion between the Outer God's will and the World Will. This evil sea demon has the potential to bring about the end of the world. The most effective way to deal with it isn't to defeat it outright but to prevent its regeneration. Even with overwhelming power, if the Outer God's will and the World Will aren't purged, it will be nearly impossible to destroy it completely.)]

"This is going to be a tough fight," Akira muttered, narrowing his eyes. But it wasn't a fight he couldn't win. If the sea demon could surpass the limits of its level, so could he!

[Boost! Boost! Boost! Boost! Boost! Boost! Boost!]

The voice of the Boosted Gear echoed continuously as Akira's body began to grow. Within seconds, a massive, 200-meter-tall crimson mecha stood before the sea demon.

[Boosted Gear's Arms—Giant Robot Mode!]

[Welsh Dragon Balance Breaker—Guardian Robot Mode!]

The giant robot's arms, back, chest, and waist all opened up, revealing countless weapon ports.

"Boom! Boom! Boom! Boom!"

Energy bombs, lasers, flames, and lightning rained down on the sea demon, shattering the sky and splitting the earth. The attacks landed simultaneously, but the sea demon simply curled up into a ball, its natural defense mechanism.

Despite the barrage of attacks, the sea demon's injuries were minimal, and it was already regenerating at a visible rate.

"Tch," Akira clicked his tongue. The thick armor on the giant robot's arms opened up.

[Weapon Transformation Loading!]

[Holy-Demonic Dragon Sword—Transformation Complete!]

In Akira's hands appeared a massive sword over 100 meters long. After transforming into the giant robot, his weapon had also grown in size.

[Secret Sword Technique · Piercing Strike!]

With this technique, Akira could concentrate all his force into a single point, maximizing his attack power.

"Slash!"

The Holy-Demonic Dragon Sword cleaved the sea demon in two. However, before the two halves could even hit the ground, they reached out and fused back together, completely regenerating.

"So that's how it is," Akira muttered. "I thought the Holy-Demonic Dragon Sword would be enough."

Without an attribute that could counter the sea demon's regeneration, dealing with this monster that was enhanced by both the Outer God's will and the World Will was going to be a pain.

Just as Akira was considering using his ultimate move, Agumon's voice reached him.

[Akira! I have a way to deal with this monster.]

[If you can cut off one-fifth of its body and prevent it from regenerating for a short time, I can completely erase the Outer God's will from that portion.]

[If we repeat this process enough times, we can weaken it to the point where it can be destroyed!]

"Agumon, you can erase the Outer God's will? Good, that's great," Akira replied. "But the Holy-Demonic Dragon Sword's attack power isn't enough to stop its regeneration."

Thinking of a weapon that could counter the sea demon, Akira immediately thought of Saber's holy sword. While it might not completely counter the sea demon, it was the most effective weapon available.

As soon as Akira had this thought, Agumon tossed him a holy sword.

[The weapon you need—I've already gotten it for you.]

"Good!" Akira grinned.

[Weapon Transformation Loading!]

[Excalibur—Transformation Complete!]

The massive Holy-Demonic Dragon Sword in Akira's hands transformed into a golden Excalibur. Akira's weapon transformation ability wasn't just about wielding weapons—it allowed him to fuse them directly into his arsenal.

Raising the giant Excalibur, Akira chanted:

[I hereby swear—]

[I will not allow anything in this world to exist that I cannot cut.]

[This sword is the blade that can sever and cut through all existence on earth! The blade of a natural enemy!]

[Divine Skill—Rending Steel Claw!]

Under the influence of this divine skill, the giant Excalibur was enveloped in a dense, black aura. Pure steel—steel refined to its absolute limit.

This skill was incredibly powerful. If Akira had a deeper understanding and mastery of it, he could have defeated the sea demon with this skill alone.

The holy sword came down!

"Slash!"

The giant Excalibur effortlessly cleaved through the sea demon's sturdy body. Even in its defensive, curled-up state, the sword cut through it like butter.

"Screeeeech!"

The sea demon let out a painful roar, instinctively trying to heal its wound. But this time, its tendrils couldn't reach the injury. The holy sword had sealed part of its regenerative abilities, and the lingering power of Akira's divine skill continued to tear at the wound.

[Akira actually severed the connection to the World Will?]

[A divine skill? When did he obtain and master something like this?]

[No, now's not the time to focus on that. This is Akira we're talking about—creating miracles is just normal for him!]

In a flash of white light, Agumon's figure rapidly grew in size.

[Gigantification—Mechanical Dragon!]

The divine flames ignited and condensed.

[Ultimate Flames!]

[Stack!]

[Tera Flare!]

A massive golden fireball shot out, accurately hitting the portion of the sea demon that had been cut off. The ultimate flames burned away the sea demon's flesh, while the Tera Flare weakened and eventually erased the Outer God's will attached to it.

[Akira! The Outer God's will in this portion has been erased! Ready for the next wave!]

"Got it!" Akira steadied himself and charged forward again.

This time, the sea demon didn't attempt to fuse its severed parts. Instead, it chose to regenerate on its own. The one-fifth portion that had been cut off was completely destroyed, so it focused on regenerating the rest.

Looking at the fully regenerated sea demon, Akira let out a sigh of relief. Although it had recovered, the Outer God's will had been significantly weakened. A few more rounds like this, and the will would be completely eradicated!

"Screeeeech!"

The sea demon seemed to realize this as well. It curled up and began to retreat, secreting a sticky fluid as it entered a state of suspended animation. In this state, its defensive capabilities were greatly enhanced.

"It seems it's realized I can't maintain the giant robot form for long," Akira said with a smirk. "Smart move. But you weren't this clever when fighting Saber and the others, were you?"

The sea demon, having fused with a portion of the World Will, had become a kin of the world. It understood that the weapons of the Fate world couldn't effectively harm it. With its near-infinite regeneration, it could afford to be reckless.

"In that case, don't blame me for bullying you!" Akira declared.

[Twelve-Winged Fallen Angel Form! Activate!]

With a loud roar, twelve dark wings sprouted from Akira's back. Since Akira was in his giant robot form, the wings were proportionally massive as well.

The Twelve-Winged Fallen Angel split off from the giant robot, wielding the holy sword, while Akira himself retreated to charge up his next attack.

[Boost! Boost! Boost! Boost! Boost! Boost! Boost!]

A massive fireball, over 100 meters in diameter, began to form in Akira's hands, growing stronger with each boost.

"Akira! I'll focus on erasing the Outer God's will. You handle destroying the monster's body!" Agumon instructed.

"Got it!" Akira replied.

As Akira focused on charging his ultimate flames, the Twelve-Winged Fallen Angel charged forward, swinging the holy sword with devastating force.

The sea demon and Akira were both relying on sheer power to surpass the Devil King level. But the Twelve-Winged Fallen Angel was different—it possessed power that far exceeded that of a Devil King!

The 200-meter-tall Fallen Angel raised the holy sword and brought it down on the sea demon's suspended form.

[Excalibur!]

The holy sword cleaved through the sea demon's body, leaving a massive wound that refused to heal. The battle was far from over, but Akira and Agumon had found a way to win.

Note: So far this story is published up to chapter 100 on my patreon go take a look and remember if you reach 210 stones of power I will publish the next chapter.