After completing the Final Singularity…
"Fou… fou? Fou… kyu kyu!"
Uhh…. God, everything hurts… What happened?
The boy stirred, opening his eyes, only to be met with another pair staring back at him with a mix of worry and relief.
"Senpai! Thank goodness you're awake!"
The girl almost yelled in relief, tears forming in her eyes. She moved in and hugged the boy with all her might.
This girl is… Mash. She's alive?
A moment passed before he realized. SHE'S ALIVE!
"Hugging you back!" The boy nearly jumped back at her, embracing someone he thought he had lost.
"Yes, good morning Master! I made it!" Mash said with a bright smile.
The boy let go of his kouhai and asked the question that was bothering him.
"Mashu… I… This is so wonderful! But, what happened to you?" The boy was greatly relieved that his kouhai was alive but was also intensely curious on how she survived Goetia's Noble Phantasm.
"Well… I really don't know myself. When I came to, I was standing at the Rayshift coordinates."
She cocked her head in thought. "I think I remember someone with a warm, kind voice sending me there, but I'm not sure."
She looked directly at the boy again. "I woke up to Fou's voice, and then I saw you running towards the Rayshift coordinates right in front of me. And something told me to reach my hand out and take yours… Fou, do you know anything?"
"Fou, fou?" The small white animal responded.
"Ahem. Hey now you two, that's enough PDA for now. I know you're relieved to see Mash alive Fujimaru, but you're making the rest of the staff uncomfortable." A female voice came from the side of them.
Both Mash and the boy released each other and the boy noticed that the entire staff was in the operations room with them.
"Sorry Da Vinci, I was just…" His words started to falter as he began to feel embarrassed at the display he just did in front of everyone.
Da Vinci gave him an amused smile. "It's fine. After all, we thought she was gone too. It's a great relief we were wrong."
She gave the boy a once over before continuing to speak. "It took you almost an hour to wake up but your vitals look fine. Your magic circuits were stressed, you seem to be fatigued, and you have a bunch of small wounds all over your body but aside from that you seem to be fine. We're all glad you made it back in one piece."
Da Vinci spoke happily towards him, but soon started to speak in a more official manner.
"Master Ritsuka, congratulations on completing your mission! With your return and awakening, I am pleased to announce our Grand Order is now complete!"
With that said the staff released some party poppers and began cheering for the mission's success. Mash looked around in amazement, while Da Vinci looked at the pair in amusement.
"The staff and I prepared this beforehand for this exact moment, although there is only a few of us, it was never going to be a thunderous applause. Buuut we wanted to make it seem like a celebration. What do you think Fujimaru-kun?"
Ritsuka had tears forming at the corners of his eyes.
"It's great. I couldn't think of anything better than this."
He was happy that the people he had spent the last year fighting alongside could all be here to celebrate their victory… well almost everybody.
Mash stepped forward happily. "Everyone… thank you… so very much. It was only thanks to your hard work keeping Chaldea safe and in a place where Senpai and I were able to return. This victory belongs to the entire staff of Chaldea. Everyone here made this possible."
After that Da Vinci went over what happened after the defeat of Goetia and what the damages were, along with a need for Chaldea to report what happened to the higher ups.
"Now that the world is back to normal, we're going to have a lot of questions to answer as well as-" She was interrupted by a sudden red glow that appeared in the room.
Everyone turned to the light's source only to find that Ritsuka was glowing and seeming to fade away slowly. Ritsuka looked at his own hand, a tired smile appearing on his face.
"Seriously, is this some plot to an anime or something?" He said somewhat self-deprecating.
"Senpai! What's happening to you!?" Mash almost yelled worriedly. She didn't seem to understand what she was seeing, mostly because it didn't make sense to her from what she knew.
Da Vinci on the other hand seemed to have an idea of what was happening. "You're going back, aren't you?" She said with a sad look in her eyes.
Mash looked between Da Vinci and her Senpai and seemed to come to a realization. "Senpai is returning to his own world!" She said with great sadness in her voice.
Ritsuka gave her a tired smile and spoke so that everyone in the room could hear.
"It seems so. I kinda had a feeling ever since Camelot, me and Ddraig talked about it for a bit and we felt like we were summoned here for a reason, although I didn't think it would be like from some isekai anime where once the job was done I would be sent back to my home."
He looked around the room before continuing. "Everyone, it's been fun working with all of you and I'm glad to have met you all."
He took a deep breath, and with power behind his eyes made this promise. "I promise to find a way back to everyone! After all, I'm sure there will be more work for us to do." He said with a wry smile on his face.
Everyone had one on as well and seemed to be content with his words. He then turned to Mash and took her hands into his.
"Mashu, we still have a bunch of trips to go on, just like we promised. So please wait for me." He tightened his grip.
Mash looked at her Senpai, smiling with tears rolling down her face. "Yes, Senpai! I will wait for you, so you better keep your promise."
On the side Da Vinci tried asking while she could. "Do you think you will be able to do it?" She was concerned that he was making a promise he couldn't keep.
Ritsuka looked at Da Vinci barely hanging on to the current plane of existence.
"You got me here once so I don't see why not. On top of that I came from 2007 in my world so if I'm going back then I at least have some time to work with. Of course feel free to try and bring me back on your end." He chuckled weakly, exchanging smiles.
"Well, it looks like I can't stick around any longer. Until the next time we meet everyone, see ya." And with that he faded from the world.
Mash stood, staring at the spot where her Senpai once stood. "I will wait for you, even if I have to wait the rest of my life." She promised under her breath.
So as you can see this story will take place after the first main arc of FGO so for those of you who are maybe thinking about playing the game and don't know anything about the story, there be spoilers ahead. For reference, not much was changed in terms of the FGO story except for small details but it doesn't amount to anything too drastic. The changes that were made will show themselves in one way or another but moving forward things will gradually escalate as the two stories happen simultaneously. This crossover is trying to be as close to the source material as possible while also making changes based on what would logically happen. I'm trying to avoid just changing events for the sake of being different although that may still happen from time to time. The idea for this is what if Issei was a Master of Chaldea and how would that change the Highschool DxD story. This idea was inspired by AthanMortis who did a Highschool DxD and Shin Megami Tensei crossover. If you read his story you will no doubt find a lot of similarities. I thought his ideas for his story were really good but I wanted to put my own spin on some of the results. As such if he does end up reading this I just wanna say big fan of his story. Anyways this story will be the beginning of Highschool DxD and the Epic of Remnant arc onwards. Also this story will be operating under the assumption that Issei has every servant available that isn't tied to the story. Also, events in FGO are unstuck in time meaning that they won't be accounted for. For events that have a specific date like the Christmas event or the .PH. event they will be accounted for since we know when it happens but events like the GUDAGUDA event will be side story stuff that have no exact date.