Summary: She thought everything was lost until her subordinate told her about a student who was in a coma for 4 months before he woke up. He showed signs of supernatural abilities and might be her only way to solve her problems. She would only later find out that the student was none other than the feared Assassin King from 1000 years ago.

"Speech."

'Think.'

Technique/Magic

Flashback/Events of the Past

Disclaimer: I don't own Naruto, High School Dxd, or other anime/manga that will be used to write this fanfiction.

Warning: English isn't my native English.

'Let's see…' thought a young man on a hospital bed. He was currently in a lotus position in the hospital room he woke up in 2 days ago. The young man's name was Naruto Uzumaki. It had been a weird experience to wake up in a body that looked exactly like himself and even had the same name. Naruto Uzumaki was a name he wielded in his past life as well.

He reckoned that he was still in the world where he died, but he woke up far into the future. When his calculations were correct, almost 1000 years passed since he died in a struggle to free himself from the chains that held him in place back then.

He once was an Assassin, the best under the heavens. There was not a single soul that didn't know of the name he earned after living as an assassin for his master, who raised him to be his tool for almost 20 years. He died when he was in his mid-thirties when he almost broke free from his master. However, the problem was that his master didn't want to let him go, so he sent multiple enemies after Naruto.

Naruto killed hundreds of enemies with his abilities as the strongest Assassin alive back then. He was feared as the Assassin King. Devils, fallen angels, yōkai, vampires, and humans knew of his existence and his abilities.

Many tried to get him on their side, but even if Naruto wanted to join their side, he couldn't. His master, who found him on the streets stealing some food when Naruto was just a little kid, placed a curse on him he couldn't break so easily.

It took Naruto 20 years to break the curse with his own power, but before he could be really free, he had to fight hundreds of enemies on his way to freedom. He killed hundreds of enemies, but after fighting for 4 days and nights, his stamina ran out, and an ultimate devil killed him.

The next thing he knew was that he woke up in the hospital room with a weak body that looked almost exactly like him when he was around 16-18 years old. The condition of his new body was terrible, to say the least.

He didn't know why he wasn't rotting in hell for all the lives he took, but he wouldn't complain. This time, he would live his life after his own decisions. Everything he would do was after his own accords. Even if he would end up working for someone else, it would still be his own choice.

But before he could begin to live, he needed to get this body into a normal shape again. He didn't have memories of the life this body had lived so far, but he knew that something messed this body up, and he was in a coma for 4 months. The coma would at least explain the terrible shape the body was in. His current body was just like the body of a 90-year-old woman or man. He had basically no muscles, and everyone could see his ribcage.

Naruto focused and began to meditate. He frowned when he felt the energy channels inside his body. They were all messed up and partly blocked. There was a lot of impure energy inside his body and even traces of demonic energy that shouldn't be inside the body of a human.

Back when he was alive, there were rumors about humans who could wield demonic energy, but Naruto never encountered one. Devils had demonic energy, but that was normal, like fallen angels or angels who had holy energy in their bodies.

'This body is more useless than I thought,' thought Naruto. He began to concentrate, and blue energy began to appear around him. 'I will use the Boundless Technique to purify this impure and demonic energy from my body.'

The Boundless Technique was an energy circulation technique Naruto created when he was known as the Assassin King. The Boundless Technique had multiple purposes. One was to boost the recovery of his body; the next one was to increase the amount of energy inside his system by drawing in the impure natural energy from the air, purifying it, and adding it to his energy. Naruto could do many things with the Boundless Technique he developed back in his days as the Assassin King. Every time he was wounded, he could help himself with the Boundless Technique. It was based on multiple energy manipulation abilities he learned over the years.

The blue energy around Naruto became stronger and lit up the room around him, bringing light into the world around Naruto. His hair began to stand up, his clothes began to move, and the air in the room began to feel fresher after the first 3 minutes of Naruto using his technique.

'The air is becoming gentler, and the menace in the air slowly fades away…' thought Naruto. Natural energy wasn't just a type of energy one could use when someone mastered energy manipulation. Natural Energy was filled with the menace of the world itself. Natural Energy draws in the menace of the living beings of the world and becomes corrupted. This was one of the reasons why there weren't many people who could harness nature, even when they could manipulate the usual energy.

Naruto began to sweat after 20 minutes, and after an hour, he stopped. The blue energy around him vanished, and his clothes stopped moving. "Phew…" said Naruto. He opened his eyes and looked at the ceiling.

"Is that is? I guess I can't expect more with this body for now," said Naruto. He looked to the side, seeing the night sky. He was still not sure what would await him in this new life, but he would live this life the way he wanted and not how someone else.

"Is that true? Naruto Uzumaki woke up from his coma and used some unknown energy manipulation technique?"

"Yes, Buchō. I felt how he drew natural energy into his body and cleansed the air around him. I never felt something like that. He managed something never seen before. I… I still can't believe it," said a young girl.

The young girl was Koneko Tōjō, a first-year student at Kuoh Academy. Koneko was a petite girl with white hair and gold eyes. The front of her hair had two long bangs going past her shoulders and several loose bangs hanging over her forehead, while the back had a short bob cut. She also wore a black cat-shaped hair clip on both sides of her hair. She wore the Kuoh Academy girls' uniform consisting of a white long-sleeved, button-down shirt with vertical linings, a black ribbon on the collar, a black shoulder cape and matching button-down corset, and a magenta skirt with a white underskirt beneath it. But Koneko didn't wear the shoulder cape like other female students.

"He seemed fine even after drawing in natural energy from the air for an hour. All my senses were working overtime, feeling this peaceful aura from the direction of the hospital," said Koneko. Koneko wasn't just a devil but also a Nekoshō, a high-yōkai. Yōkai had a born sensitivity for natural energy. Not many could even feel natural energy at all. This was also one of the reasons why mostly only Yōkai used natural energy.

"I see…" said a beautiful young woman.

The room was lit only by a few candles. Right in the middle of the room was a table with a candlestick momentarily illuminating it. Right and left was a black leather couch, which four people fit on. Directly behind the table and further along, the room's back wall was a solid wood desk with elegant carvings carved into the wood. Behind the desk was a single leather chair where the person speaking to Koneko was sitting. There was another window in the room with curtains on it. There was even a functional shower in the right rear corner. Directly next to the double doors that led to the room, there were cupboards for books, glasses, and other things on the right and left. Pictures of landscapes or houses hung on the walls, which did not appear to be of that age. There were also some animals in the landscapes that shouldn't have existed then.

The person sitting on the leather chair at the desk momentarily looked into Koneko's eyes with her blue-green eyes. She was a beautiful young woman with a voluptuous body, white skin, and blue-green eyes. She had a very curvy figure with massive breasts, unlike Koneko. Many say this woman was the number 1 beauty at the Kuoh Academy. She wore her usual attire, which consisted of a white long-sleeved, button-down shirt (short sleeves for spring/summer), with a black ribbon on her shirt collar worn under a black shoulder cape, and a matching button-down corset, a magenta skirt with white accents, and brown dress shoes over white crew-length socks. This was the standard school uniform of the Kuoh Academy for females. After all, this woman was a student of the Kuoh Academy.

Her name was Rias Gremory, and she was the sister of the current Satan Sirzechs Gremory or Sirzechs Lucifer. She did not view her peerage members as servants but as family members. The Gremory treated their peerage members as a second family, not servants or enslaved people.

Rias Gremory leaned back in her leather chair and looked at the book before her. It was just 3 days ago when her Pawn, her strongest family member, betrayed her and left her side forever. There was no turning back from the decision of her former pawn.

She was safe thanks to her since she was so strong that no one dared to approach her and her peerage. She was the target of many devils or other supernatural races. Many devils targeted her and her peerage in specific since there were many beautiful women and not a single male, making it the perfect target for those asshole male devils who told everyone that they would have the harem with the most beautiful woman.

She got many offers to join various devil families or got marriage proposals. Of course, she denied everyone and even the arranged marriage was placed on hold thanks to Rias' former pawn. The devil who was planning to get engaged to Rias knew he couldn't take Rias by force since this was the only way to have her as his wife, officially without turning Satan himself into his enemy.

If word came out that Rias lost her strongest peerage member, the arranged marriage would come back to the surface, and Rias knew she couldn't win against the asshole who could take her by force if he wanted to.

So far, no word has come out of the betrayal of her pawn, but she couldn't keep this information hidden forever. She needed more power quickly. So far, she had Koneko as her tower, one knight, one Bishop, and a queen. Formerly, she also had a Pawn who took up all 8 Pawn pieces, making it evident that the Pawn was a very strong member of Rias' peerage.

Rias sighed, looking into the eyes of her loyal Tower. "Thank you for the information, Koneko. You can go; I will send my familiar to watch over him," said Rias with a slight smile on her face. Koneko knew of the position she and her peerage members were in. She didn't want to get forced to be part of anyone else's peerage other than her Buchō.

"Okay," said Koneko. She turned around and walked out of the clubroom, closing the double doors behind her. Rias sank further into her leather chair. 'I don't have much time… I and the others need to train harder than ever before. Riser will get wind of what happened three days ago, and then he will be back in my face, forcing me into a ratting game I can't win yet. Riser has a full peerage without missing a single member,' thought Rias.

She sat up straight, summoning her familiar with a red magic circle that appeared over her right hand. A little bat-like creature appeared over the red magic circle, looking at Rias. "Please go and watch over Naruto Uzumaki," said Rias. The bat-like creature made some noises before flying out of the window.

'This again?' thought Naruto. He looked at the window, seeing nothing particular, but he knew someone was watching him. Naruto had three main abilities that made it possible for him to earn the nickname Assassin King. The first was the Boundless Technique to help him recover, and the next was an ability called Hypersensitivity, which he got from living on the edge of death for many years. All his senses were so enhanced that he could sense everything around him. He could smell, taste, hear, look, and feel more with a slight touch. All 5 of his senses were increased dramatically with the second ability he developed over the years.

With those two abilities, he managed to stay alive for all the years he was an assassin. When he was injured from a mission, he could recover his body with the Boundless Technique, and his Hypersensitivity helped him remain alive with his enhanced senses.

The third and last component was his combat abilities, which he called Dark Shadow Arts, combining multiple combat abilities to form his own unique fighting style as an assassin. With it, he became feared as the best Assassin.

'Is this a bat or maybe a bird?' thought Naruto. He woke up a week ago in this new body, having come to terms with his new situation. He still had a lot to learn, but he was always someone who was able to adapt to every situation swiftly. Otherwise, he wouldn't have made it this far 1000 years ago.

He could feel that someone was watching him, but he couldn't see the thing. He could only sense it and the magic energy it radiated, mostly from being invisible or camouflaged by some sort of magic. He sat on his hospital bed, looking at the window. It was in the middle of the night, letting him think about things he could do. He already did everything he could for now. He had used up all the stamina he currently possessed. It took a long time to repair his broken energy channels and to cleanse his energy from any impure or demonic energy.

He lay down, covering himself with a blanket. 'I should sleep. I have enough time to work on my body tomorrow,' thought Naruto.