So, this was something I've been working on in a snippets and omakes thing on another website. I've been really investeted into it and already have a lot of future chapters planned, so I decided to upload it here. But a few things before I start.

1. There will not be any sex scenes, people trying to seduce Sonic? Yes, but no sex scenes.
2. Romance will be a thing, but not a big focus. I have no issue with Sonic having a relationship with a human, I am in the camp of "If they're both sentient and agree on it, its fine". If Sonic works well with another character, there is a chance of a relationship.
3. Sonic will NOT be overpowered! He will be very strong, but many Servants will kick his ass. This will not be a story of an OP Sonic beating everyone's asses, but he will change the plot a lot.
4. It will start with just Sonic in FGO, but stuff from his world will start appearing. Characters I'm not so sure on.
5. There will be MASSIVE changes because of Sonic's presence, so you can consider this an AU of FGO.

I'm mixing the Comics, games, some of the Sonic X anime, and a few bits of fan stuff (No new Sonic characters or anything, but more just fan theories on how stuff works or what a certain thing is).
I will not say exactly when in the timeline this Sonic comes from, as new games (Or hopefully the Frontiers updates) may come out and change a lot of things. So if Sonic suddenly gains an ability from a new game or something, you know why.

For those wondering, this was inspired by the amazing MySonicFan's "Life as a Chaldean Master" and "Sonic Grand Order", which I really suggest checking out!

Sonic the Hedgehog had been having an boring day! Egghead had been basically AWOL ever since the Starfall Islands (That... had been an adventure and a half, he had actually missed Shadow of all people during it! Although a part of him had to admit the Ultimate Lifeform's power would've been nice...).

Sonic ran through the fields of Green Hill, Tails had apparently been working on some big invention with the Chaos Emeralds and had asked him to come watch. He was proud of his little brother, Tails had really been taking big steps into maturity, even if Sonic would miss the days when Tails asked him about everything.

In just a few seconds he had arrived at Tails workshop and smirked, that was five seconds shorter then previous record! With a pleasant sounding hum, he opened the door to the workshop and let himself inside.

"Hey little bro! You got an experiment to show me?". Sonic asked aloud and looked around, the Tornado was here along with some kind of... Was that a throne from Starfall island!? Sonic zipped over and began inspecting it. It certainly looked like one of those pillars throne things (What had the End called them again? Just portals if he remembered correct).

Tails was experimenting with Cyber-Space? Well if anyone was smart enough to do it, it was certainly his little brother! Sonic looked around the room for anything else of interest and smiled at the sight of seven familiar gemstones inside some kind of machine. He placed his hand on the glass separating the Chaos Emeralds and felt the familiar pull of their power.

There really was nothing else like flying about as Super Sonic, the freedom of the air in his quills, the sights he could see! Not to mention the rush of defeating whatever monster he was facing at the time! There were few times the Emeralds power had failed and just being near them gave Sonic a rush of confidence and excitement. Maybe after Tails experiment was done, he could use the Emeralds for a fly about?

He looked around for anything else interesting in the lab, the machine containing the Chaos Emeralds had multiple thick wires (Seven he noticed, seemingly one for each Emerald), connecting it to the Cyber-Space portal. There was also a couple wires going across the throne-like structure, some actually going into the throne, there was also a couple wires connected to a laptop. Sonic couldn't help but wonder what as Tails after? A stable portal to Cyber-Space? Clues about The End? Or just some of the Ancients miraculous technology? He'd just have to ask when Tails got back from wherever the fox was.

However Sonic really wasn't the best at waiting, so he began looking around for anything else of interest. Some notes from Tails, drawings of Cyber-Space and photos from the Starfall Islands, a photo of the Phantom Ruby. Oh? Now that was something of interest.

Sonic grabbed the photo of the Ruby and looked at it, frowning slightly. His first experience with the Ruby hadn't exactly been a good one and he was confused why Tails had a photo of the Ruby with the Starfall island stuff, maybe he had noticed some connection the hedgehog hadn't? The Phantom Ruby's virtual reality had been pretty similar to Cyber-Space...

It would also help explain where the Phantom Ruby came from, if it was a creation of the Ancient's meant to combat The End. He shivered at the idea of one of the Titans using the Phantom Ruby against him, Super Sonic was strong but the Ruby was... well the Ruby!

He heard the sound of the door opening and quickly put the photo back, while Tails wouldn't mind Sonic going through his stuff, the little fox had also complained about it way to many times. Sonic turned to meet the recently arrived Tails.

"Sup bro, so whats the newest machine do?". Sonic smiled, quickly grabbing one of the chairs around the lab and sitting down. Tails smiled brightly and began speaking.

"It's amazing Sonic! I've been researching the Ancients technology and Cyber-Space is unlike anything I've ever seen! It's actually an artificially created dimension that lines up perfectly with Mobius, letting it absorb information from all over the planet! It may even be connected to other dimensions like Blaze's, or even Silver's future timeline!". Tails amazement could be heard in every word and Sonic had to agree, something connecting to not just the entire planet but also an alternate dimension? He'd dealt with a lot, but that had to be one of the biggest things!

"Sounds amazing bro! Bet even Egghead hasn't figured out as much as you have". He said, causing Tails to giggle and rush over to his laptop, turning it on.

"I've been trying to figure out how to stabilize a Cyber-Space portal. Speed is obviously a way out considering how you got out, but Chaos Energy should also work! The Chaos Emeralds already have space warping properties, so if we combine them with the Ancient's technology in a controlled environment, it will open a stable portal to Cyber-Space we can safely enter and leave!". Tails smiled, he was confident and proud of his latest creation.

Sonic smiled and pat Tails on the head, drawing a laugh from the kit. He had honestly enjoyed running through Cyber-Space and wouldn't mind if Tails could make a more stable path there.

"That's amazing little buddy! It'd be awesome to explore Cyber-Space in a less stressful situation!". Sonic quickly stood up, excitement beginning to run through his body. "How about you start this little experiment and we take a jump in?".

"Sonic your the only one who can get out if something goes wrong, so maybe its best to not jump in?". Tails tried convincing Sonic otherwise, but he already knew his brother would jump in the moment the portal was stable. But he'd wait till the portal was stable... right?

Tails started typing things on the laptop, Chaos Energy started travelling down the wires into the throne, which started to glow with multiple colors and slowly, a rift appeared on the throne. It started expanding slowly, a baseball size at first, a basket ball, and after a few more moments, the size of an average mobian.

Sonic's feet started tapping against the floor, he was eager to dive into Cyber-Spaces but was waiting for an okay symbol from Tails.

"Portal seems stable, energy is at 80%... Connection to Cyber-Space is complete, its working Sonic! It's really working!". Tails laughed happily, his project was a success! They now had access to Cyber-Space! Sonic however...

"So it's perfectly safe for me to enter then bro?". Sonic grinned and leaped forward, and just when he entered the portal...

Chaos Energy did not earn its name simply because it was powerful, its the energy of Chaos itself. It did not have sides, it did not have sentience, it was just the infinite power and potential of Chaos.
Perhaps some greater entity had planned this, perhaps it was just a mistake in the calculations, or perhaps it was simply Chaos enforcing itself as a force to not be controlled. But the Chaos Emeralds began the glow brightly, the power of Chaos filling the room.

Sonic and Tails only had enough time to widen their eyes before the hedgehog fully entered the port, which glowed a blinding white, Sonic felt the familiar feeling of the Chaos Emeralds warping space-time around him and...

After the bright glow faded away, Tails quickly looked around his lab, Sonic had disappeared (He was fine, Sonic had survived Cyber-Space before and would probably be somewhere in the Starfall Islands), but something just as worrying had happened. The glass container that had contained the Chaos Emeralds was shattered, the Chaos Emeralds missing to who knows where.

"Oh no!". Tails quickly grabbed the Chaos Emeralds detector and got onto his plane, he'd travel to Starfall islands first as that was likely where Sonic would show up. If he couldn't find Sonic, he'd need to find the Chaos Emeralds and repeat this experiment. Maybe he should've been more panicked, but when you live the life of a hero, you start getting used to this sort of thing... Not that it stopped the more subtle amount of panic forming in Tails gut.

Da Vinci, head scientist of Chaldea (and the Universal Genius!) frowned. She had been performing the usual tests on the Coffins to ensure they'd be ready for when Chaldea would begin its mission, but had quickly been distracted by... Something else, all her energy reading tools had malfunctioned thanks to a wave of unknown energy (It wasn't mana, it wasn't divinity, it was unlike anything she had ever seen!).

The director had quickly ordered her to investigate and she was more then happy to do so, which was why she was currently exploring the Arctic wasteland around Chaldea, it was a bit chilly but nothing bad for a Servant like her. She had managed to repair a small energy reading tool in her staff and was approaching the biggest source of the unknown energy.

What would she find? She had no idea for once and it excited the Caster like nothing else. It was rare for the great Leonardo Da Vinci to find something she was absolutely clueless about and she was eager to tear into this mystery.

However as she got closer to where the energy originated, she would find something... Very unexpected. She stared down at the blue furred (Quills and fur she mentally noted) humanoid hedgehog, she was a Servant she knew some things existed beyond the understanding of the current world. But she detected nothing supernatural about this creature... But science did point towards its existence, she checked her radar and confirmed it, this creature was the one giving off the energy.

She had expected an object to be the thing giving off the strange energy, not a living creature and he was certainly living. In fact, despite it being the winter arctic, his body was in remarkably well condition, just slightly colder then his body size suggested (He ether had a very high natural body temperature, or the energy was protecting him).

The mages of Chaldea would likely throw a fit, demanding the creature be handed over for dissection and whatever other methods of experimentation they could think of. But Da Vinci wasn't about to let such an intriguing entity die to feed the ego of some random magus, his gloves and shoes told her he was sentient but whether he spoke a language understandable by anyone would be the real question.

Oh this was really proving to be such an intriguing event! She'd have to talk to the Director about being the one in charge of dealing with this, most mages would make a mess of this situation thinking the hedgehog was some type of phantasmal. But Da Vinci was never a quitter, she'd get her answers.

Who knows? Maybe this hedgehog could become a master? She laughed at the thought before grabbing the hedgehog and walking back to Chaldea, she was going to have some very interesting conversations with the Director!