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Disclaimer: I do not own High School DxD. I only own the OC Damian Mammon-Lucifer.

"This is so ridiculously pathetic that it's just sad and not even funny." Damian remarked with a scoff while shaking his head as he stood on a hill, looking straight towards Kuoh Academy which had a barrier in place. But through the barrier was the ongoing battle between Rias Gremory, her servants, as well as two Exorcists of the Church against the Fallen Angel Kokabiel.

Their attempt at defeating the Cadre was laughable that Damian couldn't even find the will to laugh because of how ridiculous it was.

Rias was the younger sister of Sirzechs Lucifer, who is powerful with his use of the Power of Destruction that he inherited from his mother along with his other demonic power and strength. So it would stand to reason that his younger sister would be just as strong and powerful with her mother's clan ability, right?

Wrong.

She was so damn weak that Damian wondered how she hadn't been killed ages ago. Most likely because her enemies would realize that in doing so they'd piss off the so-called 'Lucifer'.

And don't even get Damian started on her other servants.

A couple of months have passed since Damian ventured to Kuoh the first time and slayed Raynare's group, sparing only Raynare herself due to Azazel leaving her in his custody due to her now being rogue and unable to return to the Grigori lest she want to die early. In his spare time, Damian had ventured to Kuoh and watched the Gremory and Sitri groups, hidden but watching, making his own opinion of each and every single one of them. He was barely even detected by Rias when he decided to test her by seeing if she could sense his presence, but she didn't even sense him at all.

And he was in the Occult Research Clubroom while she was taking a shower!

He hadn't anticipated her to be in a shower, so it had been a surprise for even him. Especially with the fact she left the curtain open, which let him involuntarily see her naked, wet body. And yet, still she did not sense his presence when he was in the very same room with her.

She was pathetically weak for her age, and Damian knows other Devils that were more powerful and stronger than her at her age.

Although, he will admit she is quite a beautiful young woman. She sure inherited her mother's beauty, that's for certain. And there had been a dark part of Damian, a dark whisper in the back of his mind that told him to seduce Rias, to take her to bed and hurt Sirzechs in the same way that the bastard had hurt him. Images of Rias moaning and writhing in blissful pleasure had flashed through his mind, Sirzechs' reaction to finding out. Damian was a Devil, such actions weren't above even him...

But Damian had quickly banished such dark thoughts with a fierce ferocity.

Rias may be Sirzechs' little sister, but she had nothing to do with what happened between Damian and Sirzechs. As much as a part of him would want to hurt Sirzechs that way, he would not do that to a young woman that didn't even know of what her brother had done.

And Damian could also see how much Rias cared for her Pawn, this generation's Red Dragon Emperor. No matter what, he would not let any other suffer through what he had by taking one's lover and sleeping with them. He wouldn't wish that on anyone. It would make him no better than Sirzechs and Grayfia if he did.

No, it was an issue that would remain between him and them. No one else needed to be hurt or involved just to get back at the other.

'Now... what to do here?' Damian thought with his frown deepening as he continued to watch the fight, if it can even be called that. Kokabiel was just messing with them, not taking them any seriously when it was clear he could eradicate them with ease.

If only Rias' Queen, the half Fallen Angel, and her Rook, Kuroka's sister, stopped holding back, then maybe she'd have a bit of a chance. She would've had more of a chance against Riser Phenex if they stopped holding back.

The Devil of Death let out a sigh as he kept watching. No matter his opinions, he couldn't let Kuroka's little sister die when he could've prevented it. She would never forgive him.

So with that in mind, he moved.

"ISSEI!" Rias Gremory shouted as she slid along the floor and caught her pawn, Issei Hyoudou, before he could hit the ground, cradling his head in her lap as he tried to catch his breath.

"Rias," He winced out as she cupped his face and looked around on the battlefield. All her peerage members were current down and out for the count. Her Knight Kiba Yuuto, Bishop Asia and Rook Koneko Toujo were unconscious to her left with her wounded Queen, Akeno Himejima standing protectively in front of them.

To her right, the Church follower Irina was out for the count while Xenovia was barely standing and using the Durrandal to keep herself up right. Looking behind her she looked towards Sona and her Peerage and could see the sweat along their foreheads. They would not be able to keep the barrier up for much longer.

"Stay behind me, President." Her Pawn told her as he shakily stood back up and the gem on his Boosted Gear glowed.

"No, Issei! You're not strong enough." She said, grabbing his arm tightly. "You'll die in your current state."

In front of her, the Fallen Angel Kokabiel was laughing as he began listing reasons why he would not fall and how he would make their deaths as painful as possible.

"Stay with me, Issei. Stay with me," Rias whispered to her Pawn as she held her arms around Issei protectively, daring the Fallen Angel to make a move.

"Time to die. Gremory!" Kokabiel called out as light weapons appeared all around him. All Rias could do was gulp and grip Issei even tighter. It was times like this that she wished she was not so weak. Why she couldn't be more like her brother and sister in law?

"Enough."

The voice was quiet and low, yet it spoke with intensity and authority as a blast of dark, demonic power shot towards Kokabiel who was caught off guard and was only a second away from being struck had he not quickly deflected the beam with a light shield. However, as soon as he dispelled the shield and looked for the mysterious attacker, he yelled as a dark spear went straight through his left shoulder and out the other end, blood splattering out and onto the ground below him while he held a hand to the gaping hole in his shoulder.

"WHO DARES INTERFERE?!" Kokabiel shouted in a mix of pain and fury, more so fury as it was outweighing the pain.

"That would be me." A voice said and everyone turned in the direction it came from, but then a blur smacked into Kokabiel, taking him right out of the air and sending him crashing into the ground. The impact shook the ground as a crater was left in the Fallen Angel's wake.

A figure then landed between Kokabiel and the young Devils, who were unable to see the mystery man's face. All they could see, from the back of him, was that he was wearing a black, leather long trench coat with a hood that was up. And when his coat flowed to one side, they saw he was wearing black cargo pants and black combat boots. He also wore a pair of black fingerless gloves.

"This pathetic show ends now." The man said in a hard tone.

"Fool!" Kokabiel got to his feet, his eyes blazing with fury as he glared at the Devil. "Don't you know who you're messing with?!"

Light sword appeared all around Kokabiel in a circle before, with a thrust of his hand, he sent them straight towards the mystery Devil who scoffed in amusement as he readied himself.

As he stared at the light swords coming towards him, Damian summoned swords made entirely of both darkness and light to counter Kokabiel's. The Fallen Angel's swords were destroyed in seconds after a few clashes.

"Cute." He muttered under his breath, then released a part of his demonic power.

The moment he did, anyone that was still on their feet were immediately forced to their hands and knees as a pressure slammed down into them. A pressure that no one had ever felt before. Even on the rooftops, Sona and her Peerage were forced down to their knees and in doing so they unintentionally released the barrier.

Kokabiel, although sweating, struggled but managed to make it to his feet albeit barely.

Rias, who was struggling to push herself up off her front, swallowed a nervous and fearful lump in her throat as she felt the mysterious man's power. It made her own look like kindergarten levels. The only one she knew with power to match and equal this would be her brother.

Damian summoned Mortem in a flash of black and white light, twirling the demonic-holy sword around before resting it on his right shoulder while the temapture dropped to cold degrees, making the younger Devils tremble and shiver.

As if death itself had walked over them.

In the blink of an eye, Damian disappeared and was beside Kokabiel, who grunted in surprise as he turned only to yell in pain when Damian swung his sword and slashed him across the right eye. The Fallen Angel fell to a knee, clutching the heavily bleeding wound while Damian stood over him with a bored look. His coat hood had fallen down, allowing his short black hair to flow in the breeze, his hazel eyes cold and emotionless.

"So many times I've been hearing about your childish temper tantrums, Kokabiel." Damian said, shaking his head in disgust. "Tanrum after tanrum about how the Great War ended. Of how bored and disgusted you are with the peace. I've had enough, and it's time someone just shuts you up."

Kokabiel gritted his teeth, looking at him with a bloodshot eye, before he yelled as he lunged while creating a Light Spear, intending to drive it through this Devil's heart before he even realizes-

SHLING!

The eyes of every person in the area went as wide as dinner plates while Damian was calm, expression cold and unfeeling. His sword dripped with blood as he looked at the headless corpse that was Kokabiel's body. The head having fallen off, and the body soon dropped a couple of seconds later.

Flicking the blood off his sword, Damian slung it across his back and rolled his shoulders.

"Who is he?" Rias whispered, her beautiful blue-green eyes staring at their saviour with awe-filled wide eyes. In awe at his strength and power, shocked at the way he easily took down and killed Kokabiel while they barely even scratched him.

After a moment of nothing but the wind being heard, Damian turned his head a little to look at the other Devils then let up on his demonic power.

Once he did, everyone felt the invisible pressure on their bodies vanish, allowing them to stand which they slowly did while the temperature returned to normal.

Rias had her eyes on the mysterious man who didn't look at them as he began to walk away.

Rias turned to her servants. "Are you all okay?" She asked, quickly checking on each of them. Once she was certain they were safe and alive, although hurt from the battle, she gestured for Akeno to follow while heading towards the Devil that saved their lives.

To her left, she saw Sona doing the same along with her Queen, Tsubaki.

"Wait!" Rias called, making the mystery Devil stop.

Damian had known they would come after him in an effort to gain answers. Rias had that Gremory curiosity, and Sona had brains like her parents and older sister. He wouldn't be surprised if she eventually found out who he was on her own.

Even though he had stopped, he didn't turn to them.

"T-Thank you for saving us." Rias said and gave a Japanese bow that was followed by one from the others. "But... who are you?"

Damian was silent. The only sounds heard were that of his coat flapping and billowing from the gentle breeze that had settled, and the wind itself. He reached up and threw his coat hood up with a grunt before finally addressing them.

"A friend... in a way." He said lowly. He finally turned to them and appraised them with his hazel eyes. He looked at Rias first. "You sure are your mother's daughter." He ignored Rias' surprised and shocked blink of her eyes to look at Sona. "And you sure have your smarts, just like your sister."

"You know my sister?" Sona asked, surprised.

"You know my mother?" Rias added, also surprised.

"I knew both of your siblings along with your parents." He said, then tipped his hood at them. "See you around."

"Who are you?" Sona asked just as he created a magic circle to leave. He turned fully to them as he began to leave, giving her a small smirk.

"Use that brain of yours, Sona. And when you find out... tell Serafall I said hello. It's been several centuries." He gave her a small wink just before he disappeared.

And left them with more questions than answers.

However, Sona's mind was quick to start racing for everything that could figure out who this mystery Devil is. Her eyes shifted quickly before she set a determined expression on her face.

'I must go to the Underworld. Now!'

And that's it for this chapter.

Harem: Yasaka, Kuroka, Serafall, Gabriel, Raynare.