Fate/Stay Night X Highschool DXD: Of Devils and Bishops

Author's Notes: Hey guys! This is my first attempt on writing a crossover between two animes. Prior to that, I read a lot of other F/SN stories and crossovers. Thanks to the amazing stories from Gabriel Blessing and other fantastic stories, I decided to write a one myself since I am also a big fan of the F/SN franchise. I then came across 'Demon Lord's champion', which inspired me to write a crossover between the two animes. For the story, I will be using Heaven's Feel route with some Unlimited Blade Works in between since my understanding of Heaven's Feel is only limited to the wiki page. As for DXD, I only read the light novel up to volume 11. Due to the ridiculous plot shield and the incompetence of the main character, cough Issei cough, I decided to stop reading. If I make any mistakes, please feel free to point it out for me, and I will make appropriate changes. Thanks for reading!

PS: I'm looking for a beta.

Chapter 1: New life

"Shirou! No…No! Please don't die. Stay with me!"

Slowly, my vision began to blur, and I knew it was time. I had tried. I had tried my best, but I guess with my death, I was still unable to protect the ones I cared deeply. Unlike Archer, I did not regret my own actions. All I ever wanted was the smiles and happiness that radiated from the people around me. The cheerful atmosphere was enough to motivate me to keep going and keep on pursuing my own ideal.

I still remembered Kiritsugu's smile ten years ago after he saved me from the fire in Fuyuki: It was genuine. The smile he held was as if he was released from a heavy burden, and the happiness somehow shined into my empty heart. That was when I decided to become a hero to save everyone. No matter how naïve and difficult the path was, I would never regret my decision.

I guess I was wrong. I didn't regret my course of action, but the fact that I failed to save my friends from danger. Death was the inevitable consequence, and I would gladly accept it.

"I'm sorry…I…"

Too late. My consciousness slipped away before I could finish my goodbye. Yeah… They were probably really pissed at me, but I mean this was the hero's path–my path. I relaxed my body as I felt myself leaving this world, leaving my friends behind.

I guess I was caught off guard at my first sight of what was supposedly hell. My image of hell was like that of textbook: red sky, hellfire, and tortured screaming. Instead, the scenery in front of me completely blew my mind. There was no way that the color white could resemble anything I knew about hell. In fact, the whiteness of my surroundings were so intense that it forced me to blink multiple times in order to adjust my dilated pupils. So here were the two questions in my mind: Where am I? Am I dead?

"No, don't worry. You are not dead or at least not yet I suppose." I jumped a little at the sudden revelation of another presence. I quickly turned to face the source of the sound, but to my dismay, no one was there. "If I were you, I will not bother looking around. You won't be able to find me."

"Who are you?" I asked carefully. The voice did not sound anything like Archer or any Heroic Spirit that I came across. While the anonymous voice could possibly be Alaya, the thought was quickly dismissed, as no one really knew the true identity of this enigma, well, maybe besides Archer. But even then I'm not sure if he really had.

"Who am I is not important right now. What matters the most is your health right now," it said with a concerned voice. I frowned slightly at the confession. What was it referring to? What was happening to my body?

"What do you mean by that?" I asked confusingly.

"You are not dead yet as of right now, but if we don't act right now, you will die for real."

"Wait what?" I still couldn't understand what it was talking about. What did it mean by 'not dead yet', and 'I will die for real'. From what little I knew and remembered, I was critically wounded and was, with certainty, dead.

"You are still alive, but dying slowly." Oh fantastic, so I guess I was still alive. Great. Rin would definitely kill me now.

At the thought of that talented mage, I could feel a migraine forming in my head. She was already unhappy when I chose to sacrifice myself to protect them, let alone dying in the end. However, that wasn't the worst part. The worst part was that I was still alive after taking a fatal blow, so I could not and did not want to imagine what Rin would do to me upon my return. Actually, now that I thought about it, I would prefer to face Rin's wrath than stay dead. I mean she would definitely shoot some Gandr at me and call me a baka few times, in the end, she would still be glad at my return. And so would I. But still, I couldn't ignore the voice in the back of my head that yelled "Scary tsunderes!"

"So what are you trying to tell me?" If I could see the face behind that voice, I was most definitely sure that a sly smile would be there to greet me.

"Ah…Well, I have a deal to make with you." I nodded to gesture the voice to continue. "I know a lot about you, including your dream to become a hero. Right now, I am going to give you another chance to live and to save lives."

"And what is the other part of the deal?" I asked cautiously. I didn't want to miss any vital information on such tempting offer. For all I knew, it could simply be a trap to trick me selling my soul or some other crazy things you see on T.V. everyday.

"You will be reincarnated into a devil." Wait a second. What did I just hear? Reincarnate into a devil? I was only joking about selling my soul to the devil earlier, so why was this happening to me now.

"And just why will I do such thing? And what makes you thi-"

"Shirou Emiya," the voice interrupted me. "I know what you are capable of. You might not believe anything I say including the existence of devils, but I don't blame you. In the near future, a war is going to erupt and it is up to you to minimize the casualties or even stop the war itself. Besides, aren't you curious about your sister?"

I was in a deep thought, debating whether or not I should accept this offer. If becoming a devil meant that I could potentially stop a war and save thousands of lives, then going with my ideal, I would accept it without a second thought. However, at the mention of Illya, my head perked up as my face was covered with a deep scowl.

"What do you want from her? Don't you dare-" Once again, I was interrupted before I could finish my sentence.

"Calm down. Illya is in a similar position as she can at most live for another month. However, she can be saved once she reincarnates into a devil. So it is up to you now. Emiya Shirou, by accepting my offer, not only you could save thousands of lives, but also save your sister and lover. What do you say?"

Honestly, I was going to accept the offer anyway because I could finally finish off what I started. But the fact that this involved Illya solidified my decision. No matter what, I would not lose them even if it meant to become a devil.

"I will accept your offer. But explain everything about the devils to me."

"You will find out everything after you wake up. I will deliver you to your master." The voice replied cheekily. Why can't people, or devils in this case, be clear for at least one time? They always leave out some important information, claiming that answers are not given but earned through self-discovery. I suppressed a sigh and nodded my head in agreement.

I guess I was following Archer's path in a way. He joined the Counter Force in hope of saving people. Instead, all he received was regret in the end as he was basically the janitor that cleaned up the mess that humans made. He saw through the true nature of humanity and realized that his ideal of becoming a hero was simply pointless.

Archer and I were similar in many ways, after all, he was my twisted future self. But there was one thing that separated the two of us: regret. I chose to become a devil like how Archer contracted with the Counter Force to become a guardian, however, I knew I would never regret my own action. I would stick to my ideal till the very end and save as many as I could.

"We will meet again in the future, as of now," the voice said, and I swore I heard the sound of fingers snapping. "I will wake you up. Good luck Emiya Shirou!"

Before I could ask anymore, the brightness of the room began to dim as darkness slowly crawled back into my vision. My body began to stir, and I fluttered my eyes opened, which may be a mistake on my part. What greeted me was a pair of big and curious purple eyes that was only inches away from my face. Swiftly, I rolled to the side and got up into a defensive stance. Or I tried to.

My muscles ached in defiance once I tried to do any sort of movement. The shirt I wore was torn and full of bloodstains, but the wounds I received were fully closed, thanks to the healing ability of Avalon. Except, my left arm felt weird, or maybe different. Ah…right. This wasn't my arm to begin with.

During a battle against Saber Alter and True Assassin, Archer's core was critically damaged and was mortally wounded. The decision of killing Sakura or saving her came up, and in the end, I chose the latter. Consequently, my decision made Archer abandon his wish to kill me. Instead, he chose to have Kotomine graft his left arm onto me, where I lost it while protecting Illya from Zuken's assault.

"Ah…so that's what it meant by slowly dying." I muttered to myself quietly. Before I lost my consciousness, I was badly wounded, and if not for Avalon's immense healing power, I would've really died. However, that wasn't the real reason I was slowly dying. With the new arm I received from Archer, I was able to access all the accumulated knowledge and history from him. But with great power, came with great prices.

To begin, it should be impossible to graft a Servant's arm onto a normal human being due to the immense power that a Servant possessed. I was lucky. Since Archer was basically my future self, the end result of the transplant was a success. But whenever I chose to access the knowledge embedded in Archer's left arm, the invasion speed of the foreign arm would increase and eventually take over my body.

So how was this going to be fixed permanently? Also, who was this girl in front of me and where was Illya? At the thought of Illya, a feeling of anxiety and anticipation washed over me. Could she really be saved too?

"Ahem," the dark haired girl in front of me cleared her throat, dragging me away from my thoughts. I guess that was good, since I ended up with more questions than I first started. "Are you Emiya Shirou?"

I turned my attention to the girl in front of me and quickly analyzed her. She seemed to be a year younger or perhaps the same age as me judging by the high school uniform she was wearing. Her violet eyes were those of dangerous and calculative, and with those glasses, sharp was the first word that came into my mind when describing her. If she was truly my future master, then I had a really good feeling about this.

I nodded back at her and stretched out my arm. "And you are -?"

"Sona Sitri" The glasses girl in front of me replied. "I was told to come here to reincarnate two humans into devils."

"Where is Illya?" I got up to my feet and asked while grabbing onto her shoulder. I had to make sure that Illya was still alive, or at the very least, let me see her body.

She winced slightly at my grab and pointed behind her, which in return, I flashed her a grateful look before I slowly limped past her.

I almost let out an unmanly squeal when the little white haired girl tackled me with full force that led me to sit down once again.

"Onii-chan! I found you!" Illya said excitingly while hugging me tightly. I had to suppress a grimace when she crushed my injured body like that. Needlessly to say, I was really glad to see her alive. I glanced at Sona, which she gave me a small smile before she looked away, opting to give us some privacy.

"Hey Illya," I ruffled her white hair and began. "Do you know why we are here?"

Illya broke apart and shook her head in return. "Someone told me that I could save you, so then I just accepted its offer," she said happily.

I let out a sigh and gestured at Sona, who was currently standing few feet away, back facing us. "I guess we can only find out after we talk to her."

With that, I made my way back to the dark haired girl with Illya trailing behind me. Upon our approach, Sona turned around to face us with her arms crossed. Before I could ask her any question, she simply raised her hand into a halt and began to speak.

"You might be wondering what is going on," Sona began as she eyed both of us expectantly. "I am looking to complete my peerage for the future participation in the Rating Games."

Wait…what? What was she talking about right now? Peerage? Rating Game? My confusion only increased as she tried to throw out some more information.

"What my source told me is that the three of you made a deal, am I correct?" Sona asked us while adjusting her glasses. Both Illya and I nodded in agreements. "However, I do not know anything about you two, so I'm not sure if the two of my bishop pieces will suit you."

"What are those evil pieces that you are talking about?" I asked confusingly.

At my question, Sona rubbed her forehead and sighed. "Right, I totally forgot about it. This is just like chess, where a full peerage consists of a king, a queen, two knights, two bishops, two rooks, and pawn(s)."

While I may not be an expert at chess, I at least understood the basic rules of it. However, what I didn't understand was the function of each piece. I narrowed my eyebrows and motioned her to continue.

"Well, I am the king piece in case you didn't know. Queen possess all the characteristics of rooks, knights, and bishops, in other words, it is the most balanced piece. Rook simply gains monstrous strength. Knight has low defense, but in exchange, it gains agility."

So the system that the devil had was similar to the Grail System after all. To put it simple, an evil piece was a catalyst for the master to summon a desirable Servant. The only difference was the fact that the master, or the king in this case, held control up to fourteen servants/pieces.

A Saber class was equivalent to the queen piece as the stats were considered as balanced. Needlessly to say, a rook was basically Berserker, minus the Mad Enhancement of course. Lancer and Rider could both qualify as a knight piece, which left us bishop as the remaining piece…

"And lastly, for bishop," Sona started to explain while playing with the two chess pieces that seemed to be bishops in her hand. "It enhances magical skills, which include wide range of spells, such as healing, defense, and offense."

Ah, so bishop was Caster. Well, I was sure that Illya would qualify for the bishop piece, but me on the other hand… I was certain that a queen piece would be best suited for me, putting into account that my fighting style was similar to that of Archer's: Suicidal.

"What about pawn?" Surprisingly, it was Illya that posed the question.

"They are slightly different from other pieces." At the declaration, my eyebrow rose, and I gestured her to continue. "Pawn has the ability to promote into a queen, rook, bishop, or knight only in the enemy territory. Besides that, they have no additional stats gain. However, do not underestimate a pawn as they can potentially be as powerful as any other piece."

With queen's enhancement, I would have power over the rook piece, which could possibly make my defense impenetrable with my own Reinforcement. The agility and enhancement of magical spells provided by the knight and bishop pieces would greatly benefit me as well.

The downside was the fact that the queen piece only possessed a small fraction of every other evil piece, which in terms made the piece itself balanced and not specialized in a certain category.

Pawn would not be a bad choice as I would be able to promote myself to the best-suited piece depending on my opponents and terrain, but only if I managed to cross the enemy territory. And knowing this specific trait of pawn, successfully promoting myself would definitely be challenging.

Just like all chess games, pawns were usually the sacrificial pieces for the future maneuver of other pieces, and I did not fancy that kind of playstyle. Though playing the sacrificial role somewhat fit me, dying first would not allow me to save anyone in the end.

So these were my options: bishop or pawn. Before I could make up my mind, Sona spoke up again.

"However, I don't think I have enough pawn pieces to reincarnate you, assuming you are as strong as my source said." Sona told me. Well that narrowed down my option. "But your abilities are unknown to me, so I can't really use up two of my pieces without seeing what you have with my eyes."

Fair enough. After all, just like the Grail War, it was only reasonable for the Master to understand the Servant's power and limits in order to plan for future battles or avoid formidable opponents. Plus, it would only be logical for a bishop to already possess any sort of magical traits, since the purpose of the piece was to enhance all magical spells.

Illya was already a powerful magus due to the fact that she was a child of a human and homunculus, which granted her more magic circuits than a normal human being. By becoming Berserker's Master, her body was modified to maximize the amount of circuits she had, making it possible for her to control the mad Servant.

Me on the other hand could also qualify as a bishop, since I was also considered as a magus. However, to compare Illya's talent and potential in magic to mine would be like comparing Heaven to Earth–the disparity was just too large. Unlike most magi, I specialized in two types of magic…

I gave Sona a meaningful nod before I walked toward the nearest tree and grabbed a fallen tree branch from the ground.

Trace on… Composition Analyzed… Reinforcing…

With a branch in my hand, I walked past Illya and then Sona, who shot me a confused look, which I returned with a smug smile of mine, before I stopped about three feet away from the tree. Looking at my target carefully, I lifted my arm and threw the reinforced tree branch straight pass the two girls.

A somewhat surprised expression was shown from Sona when the tree branch managed to penetrate the trunk of the tree, leaving a clean and hollow hole behind its path. Probably what surprised her the most was the fact that the branch I threw was still in one piece. Illya, on the other hand, was smiling and clapping her hands at my small performance. "Onii-chan is good!"

It seemed like my small demonstration did not please Sona as much as I expected considering that she concealed her surprised expression so quickly and was now replaced by an unimpressed look.

"Honestly, that wasn't too impressive," she said with a shrug. Behind her emotionless face, I could somewhat hear the disappointment behind it. Even though it was well concealed, I could tell that she was expecting something more from me. I guess I would give her more.

Without any other word, I walked back to the tree and took a close look at it. "Diameter about sixty centimeters," I muttered to myself. "Hm…this should be a piece of cake."

Once again, Sona looked extremely confused at my action, but her confusion was quickly replaced with an awe expression.

I punched the tree with my reinforced fist. And I blew it up.

The power behind my punch was almost as strong as those of weaker Servants. The impact was able to smash the tree in front of me into splinters that flew in all directions. The root of the tree was completely lifted from the ground, living a nothing but dirt in the empty hole. Right on cue, the leaves glided down from the branches slowly, giving off a dramatic atmosphere.

I glanced back just in time to catch the gaping look from Sona, who obviously didn't expect any of this to happen. Illya, on the other hand, was clapping even louder with an expression like a child who just received a Christmas present from Santa.

Casually, I walked passed the shocked devil and returned standing next to Illya. "So how was that?" I asked with a smug face. "Does that exceed your expectations?"

Apparently, she was too shocked to answer, so I had to snap my fingers loudly to bring her out of her trance. "Y-Yes," she managed to stutter the word out. "I think that will be just fine." She then shook her head and pointed at Illya. "Well, it's your turn."

I tried to suppress a grin on my face as Illya looked at me confusingly. "Oni-chan," she said while tilting her head to the side with a finger on her lips. "What am I suppose to do?"

I thought for a bit and finally came to a conclusion. "Well, why don't you just create those bird familiars for now. I think they are impressive enough," I patted her head and told her. "Ah… feel free to create some explosions," I added in the end before she created some space between the three of us.

I then turned to Sona and said, "While we are at it, why don't you show us some of your moves too. So in the future, we will be able to work out a battle plan effectively."

The nod from Sona meant that she at least understood where I was coming from. After all, if we were to be in her peerage, trust was the first thing to establish as we would be working together for quite awhile. "This is just a demonstration of power, so don't kill each other," I told the two girls when Sona walked up to face Illya. Well, to be exact, that was actually for Illya, since she tend to get all worked up when fighting. I looked at the two of them again and signaled the spar to begin.

I was really curious at what kind of magic Sona uses. The only thing that got me worried was Illya. She was easily considered as the strongest magus, even stronger than Rin. If she decided to go all out, Sona would most likely receive fatal injuries. But then again, I knew nothing about the power of devils, so my only option was to wait and see. If the situation was deemed necessary, I would have to interfere the fight to save Sona.

I shook my head to bring myself back to reality to watch the battle before me unfold. Like I instructed Illya earlier, she pulled off two strands of her hair and created the high-performance bird familiars, Zelle.

Sona on the other hand, didn't even look amazed as she was focusing on channeling her own spells. Once she gathered enough power I assumed, she raised her hand in the air and made four hawks that were transformed from water. The move itself didn't look too impressive compared to that of Illya. There was no way that it could match Illya's attack, but I decided to watch till the very end, since everything I just thought of was simply made from my own assumptions.

Once Sona was ready, she immediately began her attacks. With a swing, the hawks she made flew towards Illya. The homunculus gave a swing of her own and ordered her familiars to retaliate.

A small explosion erupted in mid air as the two creations clashed with each other. Like I predicted earlier, Illya's Zelles overpowered Sona's attack easily as the hawks she made was nothing but puddles of water right now.

She didn't look surprised by the fail attempt to strike down her opponent, instead, she was already channeling her next spell. On the other side, Illya didn't give Sona the time to finish before she ordered her familiars to strike.

Luckily for Sona, her spell was ready just when the birds were almost in range to attack. Shots of water flew out from her fingertip, forcing Illya's familiar to dodge, which bought herself some time to quickly summon a hawk to shield the attack. She then conjured a lion immediately to pounce at Illya, hoping that her attack would catch the opponent by surprise.

Sona's attacks were relentless, but the power behind each spell was not strong enough to really pose a threat. The lion she made earlier was easily dismissed by one of the Zelle as the magical familiar shot a beam of magic to destroy it. Illya then raised her arm and transformed one of the familiar into a sword, which surprised Sona greatly. Without any delay, the sword was shot forward with a speed that could possibly rival that of Archer. I palmed my face at this. Didn't I tell her to be careful?

I was about to jump into the fight to save Sona, but what she was able to do next surprised me greatly. Using the puddles on the ground from her previous spells, she desperately created a water shield that was strong enough to temporarily slow down the attack from Illya. However, that wasn't enough to stop the magical flying blade. Right when the shield depleted, Sona was able to roll out of the harm and was now staring at the white blade that could've killed her.

Even though she managed to get out unscarred, the pace of the battle was in Illya's control, which meant that there was no point of continuing. After all, this was only a small spar to demonstrate each other's abilities. And one last thing: I wanted to conceal some of our powers for future.

"Alright, I think this is enough," I walked forward and told the two girls to cease fire.

Illya turned to look at me with a small pout on her face. "But oni-chan, I was just having fun!"

"I'm sure you will have fun later on," I told her dryly. "You almost killed her." I then turned to look at Sona, who had a hand under her chin, reviewing the small duel for sure.

Despite the fact that Sona clearly lost to Illya, I didn't look down at her a single bit. In all honesty, I was quite impressed, even though I knew that Illya was holding back greatly. Considering that Illya was a first rated magus that was more powerful than Rin in certain aspects, being uninjured and blocking all damage throughout the whole fight was really impressive.

"Don't worry about the loss," I said to the devil. "We won't be fighting each other anyway. But I want to know more about the devils and this world."

"Yes, I will definitely fill you in on that," she nodded at my request.

"So how was that little assessment?" I asked smugly at her. She let out a heavy sigh and said, "Yea, I think the both of you will be good for my peerage…maybe a bit too good." I was sure that the last part was not directed to us, so I let it slip and nodded gratefully.

"Like I said earlier, I will take you under my peerage and begin the process of reincarnation," Sona said while displaying the two chest pieces in her hand. "I, Sona Sitri, hereby ask you:" As soon as she started the chant, a red magic circle appeared below Illya and my feet. "Emiya Shirou and Illyasviel Von Einzbern, will you swear upon your life to be faithful and loyal to the Sitri Clan and support your king in any possible way?" Both Illya and I nodded at the vow. "Then you shall become my bishops and rejoice in your new life as devils!"

In front of him was a wasteland, filled with nothing but swords and dead bodies. It wasn't his first time to stand alone in the mess he made, after all, he was all alone. It was his job to save. It was also his job to clean up. To save meant to kill, and he would gladly accept his own fate. It was his dream to become a hero of justice.

He had been summoned to the battlefield over and over again to save and to protect the humanity. He regretted. In the end, the person he saved betrayed him, and he was killed. He then finally realized how pointless his dream was: nothing but full of betrayal and endless pain.

He wanted to escape. He wanted it to end. But he couldn't. And so, he walked a lonely road that was full of bloodshed and betrayal.