Crossover-Isekai 300

Chapter 300 Extermination & Holy Sword

Edited by: Kanaa-senpai

 The “Hentai Heroines” Aki had conquered were perfect seeds for making Valkyries. But he lacked the power to turn them into a strong, Valkyrie-like guard.

 He did not need the power of a heaven-born god like Akira. Still, he needed the strength of a Dragon God at the very least.

 The mechanical Angels made by the Ten Core Gods reached Demon King-class. Yet, they clearly had many flaws.

 Even to revive the Red Dragon Emperor, Aki needed Dragon God-level power. No matter how “trash-tier” the Valkyrie guard might be, they were still God-tier.

 Helping these Hentai Heroines break through their limits was no easy task. They lacked natural talent. Reaching God-tier was as hard as reviving the Red Dragon Emperor.

 Such thoughts were far away for now. Aki pushed them to the back of his mind. He turned his focus back to steadily increasing his own strength and that of the girls in the Occult Research Club.

 By day, he engaged in Dual Cultivation. By night, he went out with Rias and the others to exterminate Stray Devils.

 Ever since they started Dual Cultivation, handing out flyers was a thing of the past. Accepting contracts from ordinary humans to boost their strength had also stopped. Only Yuuto still did it.

 It was not just the Occult Research Club. Even the Student Council had stopped doing them.

 Compared to the benefits of Dual Cultivation, Contracts were simply thankless work.

 If it were not for the urgent need to “Breach” her current strength, Yuuto would have stopped long ago. She wanted to return to her original female form as soon as possible.

 Luckily, her Contract clients were generally beautiful, charming city office workers. Occasionally, when he was in the mood, Aki would tag along with her.

 Usually, Aki just watched. Though, there were times when he felt a certain… chemistry.

 In those instances, Yuuto might lose a client.

 Compared to the real physical comfort Aki could provide, Yuuto’s gentle care seemed to fall just a bit short.

 …

 Just like that, time quickly arrived at mid-August.

 On a normal night, no different from any other, a long-eared elf girl was cornered. She had a delicate, cute appearance. The members of the Occult Research Club had trapped her in an abandoned factory.

 Before Aki could take more than a few looks at her, she instantly ballooned into a giant. Under the silvery moonlight, the girl had appeared purely innocent and pitiful.

 Her cute face turned ugly and hideous. A strange, strip-like bump grew from her forehead. It looked like both a withered tree branch and a twisted tentacle.

 Her originally slender frame transformed into a very disgusting, massive insect body. The two mounds of soft flesh on her chest morphed into bizarre weapons.

 The White-haired loli was on the front line. She was caught off guard and had her arm burned by corrosive liquid fired from within.

 ”Well, that really proves ‘blackened’ is ten times stronger, and ‘washed white’ is three times weaker.” Aki remarked casually.¹

 He watched Koneko as she received treatment from Asia. Aki couldn’t help but remark on it.

 The mutated Stray Devil before them had the strength of a mid-level Devil at most before. After mutating into a monster, she had actually injured an SS-Rank White-haired loli with a single strike.

 Even though she used a surprise attack, it proved that the amplification to her strength was completely absurd.

 However, she had lost her reason. No matter how strong she was, her only fate was to be eliminated. Compared to the strength of the Occult Research Club, this Stray Devil was the weaker party.

 Rias drove the ugly, giant monster to the empty space behind the factory. She used a clean, decisive strike of destructive Mana to turn it into basic elemental particles. She spared it even the process of being liquified.

 ”Buchou, why do I feel like the ones who mutate into monsters are always pretty schoolgirls?” Aki asked calmly.

 He had participated in many Stray Devil extermination missions recently. Excluding the Youkai and such, he had discovered a pattern. Among the Devils who fled from their Masters, not everyone mutated into mindless monsters.

 Many retained their reason and human form. For example, the Broom-head Devil he had arrested earlier combined Alchemy with Biotechnology.

 Then there was Koneko’s sister. She was a Reincarnation Devil who also possessed the Nekoshou bloodline. Even though they hadn’t officially met yet, the image of Kuroka was deeply etched in Aki’s mind.

 If the “butterfly effect” hadn’t interfered, this big-breasted cat-girl would eventually become the Peerage of the battle-crazed Vali Lucifer. It was precisely because she became the Peerage of this generation’s White Dragon Emperor that her act of killing her own Master and fleeing was overlooked. It was even “vindicated.”

 Had she not sought refuge with the White Dragon Emperor, the act of killing one’s master would never have been forgiven by the Devils. It did not matter how wrong her Master had been.

 ”Because these kinds of Devils generally only flee their Master’s side to satisfy their own desires,” Akeno said crisply. “They act out as unfaithful wretches.”

 ”Only Stray Devils who have lost all heart and mind will end up like this.”

 The one answering Aki wasn’t Rias. It was Himejima Akeno, who was in charge of deploying the Barrier.

 Her pure-white Shrine maiden outfit reverted to casual clothes. She dropped her combat stance. “Things like this can’t really be called Devils anymore. No wonder the higher-ups issued an emergency extermination order.”

 Himejima Akeno’s explanation was rather vague, but Aki understood nonetheless.

 Simply put, these young girls who looked pretty and cute lacked a firm mind. This made them prone to mutation. Meanwhile, individuals like the Broom-head Devil looked strange but possessed a firm pursuit in their hearts. They would not lose their reason and therefore wouldn’t mutate.

 These Devils would be sent back to the Underworld. Those who mutated into monsters were destroyed on the spot.

 This was likely the only side effect of “Evil Pieces” for Reincarnated Devils. After all, it was equivalent to changing one’s species. While it was quite magic, having side effects was perfectly normal.

 The extermination was over. One of his questions was resolved. Aki was about to head back to continue his Cultivation. Suddenly, Yuuto walked up to his side and whispered.

 ”Aki-kun, could you come with me for a moment?”

 Aki hesitated. He didn’t want to spend too much time alone with the “handsome guy version” of Kiba. But thinking about how the other had seemed to be losing focus over the past few days, he eventually agreed.

 Rias and the others exchanged glances and transmitted away. They left the space to Yuuto and Aki.

 Returning to the large mansion, they entered the room of the blonde Little Nun, Asia.

 Rias crossed her shapely legs and rested her chin in one hand. “Akeno, Yuto likely wants to talk to Aki about the Holy sword, doesn’t she?”

 ”Likely so. It seems she got some clues about the incident back then from someone named Hyoudou Issei a while ago.”

 Himejima Akeno pressed her index finger to her cheek. She thought for a moment and added, “Besides, without Koaki’s help, it really is too difficult for Yuto to improve her strength.”

 Because of the Boosted Gear, Hyoudou Issei had come into contact with the Occult Research Club many times. The girls had some impression of him, though not much. Perhaps it was less than their impression of the Pervert Trio, but his name had been remembered.

 ”Asia is about to Breach A-rank. Once she starts Dual Cultivation, I suspect she’ll be able to catch up to our pace very quickly…”

 Amano Yuuma (Raynare) paused before continuing. “Then only Kiba will truly be left behind.”

 Asia’s Mana Talent was excellent. Once she reached A-rank and completed her first life-quality transformation, paired with Aki’s Dual Cultivation, her improvement would be faster than taking a rocket.

 It was just her personality that had caused her to put all her Talent points into healing. Otherwise, she would definitely be a turret-style mage not inferior to Himejima Akeno.

 However, having a healer with a bottomless supply of milk was a massive boost to the combat effectiveness of the entire group.

 Rias stroked Asia’s smooth blonde hair and sighed. “I know, but the Holy sword is too dangerous.”

 The blonde Little Nun was being praised and having her head petted. She felt incredibly shy, but curiosity eventually won the day.

 ”Buchou, what is the Holy sword?” Asia asked innocently.

 ”The Holy sword, also known as the Sword of Kings.”

 Rias explained, “The Holy sword is the most terrifying weapon for Devils. Devils sustain damage just by touching it. If they are slashed by it, they might be directly eliminated.”

 Looking at the nervous expression on the blonde Little Nun’s face, Rias summarized. “That’s right, the Holy sword can destroy Devils.”

 ”What a terrifying weapon…”

 The blonde Little Nun pressed her hands together. She habitually started to pray. But following a sharp sting in her brain, she realized she was already a Devil. She could no longer pray to God.

 Aki hadn’t helped Asia get prayer privileges from Michael. Rather than praying to a God that didn’t exist, he felt the blonde Little Nun might as well pray to him.

 On the other side, Yuuto and Aki were saying much the same thing. Though, there were a few more supplementary points.

 —

 Summary:

 Aki continues to manage his growing harem of “Hentai Heroines” while refining his power levels through Dual Cultivation. The Occult Research Club handles a routine extermination of a mutated Stray Devil that unexpectedly displays high combat prowess. As Rias and her peerage analyze the nature of these mutations, the narrative shifts toward a looming mystery regarding the Holy Sword and the personal internal conflict of Yuuto.

 —

 Trivia:

 The mutation of Stray Devils into monsters is linked to their internal lack of conviction rather than just their loss of humanity.

 Reincarnation as a Devil using Evil Pieces acts as a species change that carries inherent magical side effects.

 Yuuto has been struggling with internal focus and combat stagnation, which is a major plot point for upcoming developments.

 The Occult Research Club members are aware of Hyoudou Issei, but he is currently ranked below the “Pervert Trio” in their social hierarchy.

 —

 Translation Notes:

Notes:

• Aki – A tall, handsome Kuoh Academy strategist and King-status devil with a powerful, dragon-like physique and scumbag-like charisma, he wields Dual Cultivation and soul contracts to heal, empower, and psychologically condition his growing harem of schoolgirl knights and supernatural companions. A master of magical tool control and Evil Piece distribution, he pragmatically expands his peerage while indulging his immense sexual stamina and appetite, balancing flirtatious charm with dominant control as he ascends toward Demon King-class power.

• Akira – A blonde, arrogant SSS-Rank strategist for the Naruse sisters, he wields the Boosted Gear, Soul Covenant, and Dual Cultivation. Connected to the yakuza and ORC, this unstable youth uses his Underworld knowledge to protect allies while building a contract harem. Driven by envy and a quest for revenge against Aki, his growth-oriented yet volatile nature ultimately leads to a tragic downfall.

• Y – The first initial/part of the name Y Ddraig Goch.

• Rias – Rias Gremory, a striking SS+ high-class devil heiress with crimson hair, blue eyes, and porcelain skin, is the head of her household and Master of Kuoh Town. As the confident, authoritative leader managing local supernatural affairs, security, and peace negotiations, she guides her peerage, mentors Aki, and maintains formal etiquette. She is tied to Sirzechs and Sona, and acts as Aki’s accomplice.

• Yuuto – Blonde, androgynous, and polite, this Kuoh Academy student is an A-Rank Knight in Rias’s peerage and Issei’s childhood friend. A Holy Sword Project survivor harboring intense trauma and survivor’s guilt, she aims to destroy all Holy Swords while investigating their provenance. Despite an analytical mind, supernatural awareness, and magic blade forging, her physical blocks stall her high potential.

• Koneko – A sixteen-year-old Nekoshou with white hair, cat features, and a petite, doll-like physique, this stoic girl serves as Rias Gremory’s Rook and a combatant in Aki’s group, with whom she signed a Soul Contract. Recently injured in battle, her usual impassive restraint yields to magical resonance during a tough gym fight, making her deeply affectionate with Aki and prone to jealousy.

• Asia – A gentle, blonde first-year nun reincarnated as a kind-hearted Devil and Gremory peerage Bishop in the Occult Research Club, now under Aki’s tutelage. With a compassionate heart and clear-headed diligence, she serves as a vital healer for trauma survivors, quietly anticipating her own growth. Her naive affection for Aki—born from a once-shared lunch—deepens as she learns under his guidance, her pure demeanor and radiant presence offering comfort to all around her.

• Broom-head Devil – A Stray Devil with a distinctive silver-haired broom-like hairstyle who is obsessed with alchemy and female breast enlargement.

• Kuroka – Koneko’s older sister is a Nekoshou with a top-tier physical figure. She possesses a dark history of killing her own master, a defining aspect of her identity that deeply shapes her past and complex relationships with others.

• Kuro – A companion or observer who hides during combat and provides information to Aki.

• Lucifer – A house name associated with the White Dragon Emperor’s lineage. An original Demon King whose lineage is inherited by Vali.

• Vali – A stoic, arrogant half-demon youth of Ancient Devil blood, this battle-crazed individual is the White Dragon Emperor, Albion. Wearing resplendent white armor with light-absorbing wings, he triggers Balance Breaker at will. Taken in by Azazel but later joining the Khaos Brigade, this cynical warrior seeks a fated rival, though Governor Shemhaza admits his actions reflect a lack of supervision.

• Akeno – Himejima, a tall, voluptuous Orc-devil shrine maiden with raven hair, red eyes, and dark wings, is the “Priestess of Thunder.” As Rias Gremory’s loyal S+ rank Queen and Vice-President, she gracefully manages administration. Beyond her combat prowess, she is the soul-bound contract partner of Akira, maintaining a deep, affectionate bond with him and constantly longing for his attention.

• Himejima Akeno – A high-ranking member of the Gremory peerage and household, this buxom female student with black hair in a ponytail assists Rias with magical tasks. Known as the Lightning Flash, her previously reserved demeanor has shifted into a sultry, energetic, and passionate personality during cultivation, maintaining close ties as a supportive ally to her companions.

• Himejima – Akeno Himejima is a tall, curvaceous Kuoh Academy senior and high-ranking Devil retainer in Rias Gremory’s peerage, bound by a Soul Contract to Aki. With long black hair and a poised, queen-like demeanor, she exudes refined grace and sadistic charm, wielding golden lightning and mastering advanced magic. Deeply loyal to Rias, she guides Aki with teasing warmth, balancing her powerful presence with maternal authority and unwavering devotion within the Gremory household.

• Kiba – Yuuto Kiba is a handsome, slender, 1.7m tall blond Devil known as a campus prince. A master swordsman and survivor of the Holy Sword Project, he is a polite, composed knight in Rias Gremory’s peerage. Despite his refined demeanor, he harbors deep-seated trauma, a strong distaste for the Church, and intense hatred toward Fallen Angels and certain priests linked to his past. Also known as Yuto.

• Yuto – A member of the Gremory household tasked with evacuation.

• Hyoudou Issei – A brown-haired Kuoh Academy high-schooler with an average build and mischievous face, Issei Hyoudou is the original host of the Boosted Gear. Infamous as part of the “Pervert Trio” for peeping on girls, he is notably unlucky but maintains close, chaotic ties with his classmates and fellow trio members.

• Hyoudou – The Hyoudou family name is carried by Issei.

• Issei – Issei Hyoudou is a brown-haired, kind-hearted Kuoh Academy student known for his lack of academic ambition, fixation on girls, and membership in the “Three Perverts.” The son of the Hyoudou family, he exhibits protective anxiety regarding his mother’s interactions with outsiders. As the host of a powerful supernatural relic, the Boosted Gear, he is the Red Dragon Emperor’s successor. He is currently captive for an extraction ritual and a source of information on Holy Sword experiments.

• Amano Yuuma – Yuuma Amano is the alias of Raynare, a Fallen Angel disguised as a school uniform-wearing transfer student with a pure, innocent face, a devilish, slender figure, long black hair, and black wings. She serves in Rias’s Peerage, the ORC, and a barrier maintenance team. Possessive, assertive, and proactive, she takes the lead in training her partner Aki, with whom she desires intimacy.

• Raynare – Lady Raynare, alias Yuuma, is a voluptuous, dark-haired former Fallen Angel training under Rias in the Occult Research Club. Shifting between an innocent schoolgirl guise and her true nature, she is contracted to her mentee, Aki, boosting her combat strength to high-end S-Rank. Though struggling to fully integrate as a peerage member, she provides vital insight into current combat dynamics.

• Amano – Raynare Yuuma, a fallen angel masquerading as a Kuoh schoolgirl, is a striking woman with long hair and a commanding presence. Secretly a Devil bound by a Soul Contract to Aki, this former Occult Research Club member possesses black-belly powers and instant-change abilities. She conceals her true faction and fears, remaining a disciplined, protective figure deeply concerned for Aki’s well-being.

• Yuuma – Amano Yuuma (Raynare) is a striking, curvaceous high-class devil, light magic master, and devoted Pawn in Aki’s peerage, bound to him by a profound soul contract. Formerly a fallen angel, Grigori operative, and involved with the local Fallen Angel trio, she has long black hair and violet eyes. Known for playful teasing, she holds an obsessive, fierce devotion and absolute allegiance to Aki.

• Michael – A handsome Archangel with a radiant aura and golden armor, this pragmatic religious figure leads Heaven and the surviving Seraphs after God’s disappearance. Possessing power exceeding a Super-Devil, he maintains the System to preserve peace among the Three Factions, prioritizing order over lives. He also aided the Holy Sword Project, modifying its rituals to prevent the death of subjects.

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Edited by Kanaa-senpai.
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