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STH: Under the foundations

Summary:

In a world subdued by Robotnik. Sonia and Manic try to hold on to the fragments of a prophecy that no longer seems to guide anyone.
Then, fate throws them two strangers... Although, to their misfortune, the face of one of them is all too familiar.
Sonic and Tails. They don't know how they got here, or how to get back. But it's clear to them that they can't just sit idly by.

A crossover between the Sonic games and the Sonic Underground series...

Notes:

I did my best here...

Chapter 1: It seems like home

Notes:

(See the end of the chapter for notes.)

Chapter Text

“Manic…”

“nanara nana nanaaa…”

“Manic.”

“mmmjmmm jmmm…”

“¡Manic!”

A green hedgehog with rambunctious spikes finally reacted to being abruptly stripped of his headphones. She grimaced in disgust, as if the best guitar solo of her life had been interrupted, but when she noticed who it was, she knew it was no time to fight. 

“Is something wrong Sis?” He asked reluctantly.

“I've been talking to you for about half an hour to start the mission and you decide to stay in the middle of Robotropolis” Sonia, the fuchsia hedgehog, crossed her arms firmly. Her expression showed more frustration than surprise. Manic looked at her without fully understanding, then looked around: the sky blackened by smog, streetlights flickering as if they didn't want to work, and the air filled with an unpleasant metallic smell. “Are you waiting for us to get caught too?”

He smiled with his typical sly grin, shrugged his shoulders and leaned nonchalantly against a yellow van parked on the side of the street. Despite the neglect of the area, the vehicle looked surprisingly well-preserved. On one of its sides gleamed a painted purple guitar, although the lettering beneath the logo appeared to have been forcibly torn off, leaving faded traces.

“Sonia... You know Buttnik doesn't care about this area. We'll be able to give ourselves the time to exploit the whole....”

“Help!”

 

Both urchins tensed. The childish cry cut through the thick city air.

“Was that a child?” Manic asked, already stowing his music player in his orange fanny pack.

“Let's investigate” Ordered Sonia with a firm voice, opening the side door of the van.

Sonia, in her red blouse, purple skirt and two-tone heeled boots, pulled her pink motorcycle out of the compartment. Manic followed her, letting his white shoes with red hit the ground as he climbed onto his hoverboard, a red one with yellow stripes.

“They better not take another step!”

They both advanced to the place when they heard a new childish voice. Luckily for them, they identified the place: it was just around the block.

When they arrived, they recognized where the danger was: a dark, dirt-covered alley, not unlike the rest of the city.

“Hey, nut head!” Sonia shouted, getting off her motorcycle and advancing fearlessly towards the aggressors, “Leave them alone if you don't want to...!”

But before she could finish the sentence, she watched in surprise as the red and purple robots began to sizzle for a second, before releasing smoke from their metallic bodies. Manic, who had already caught up with her, stood on the sidelines next to her sister, trying to make sense of the situation.

Not more than another second passed when both robots fell to the ground, emitting a beeping sound followed by a cloud of smoke.

“Have they been deactivated?” asked Manic, confused. His sister was equally perplexed, so she simply raised her shoulders in response.

“Thank you very much, I was so scared!” The childish voice reminded them of their original objective.

“Check on the SAWTBots, I'll take care of the children.” Sonia ordered. Without waiting for an answer, she went into the alley and found two little Mobians. One of them, a little fox with yellow fur, had interposed itself between the other and the previous danger. But what caught Sonia's attention was that the fox had an extra tail.

“Heh, you're welcome, little one. You didn't hurt yourself, did you?” Ignoring the curious detail of her two tails, Sonia took a step forward to be in sight of both of them.

“You know what? That's what I should be asking.” Both children were surprised by the arrival of the hedgehog but smiled kindly when they saw that the girl came with good intentions.

“I feel fine but he...” The little mobian next to the little yellow fox smiled and nodded. “Well, it looks like we're both fine. Thank you.”

Sonia nodded.

“This is interesting…” Manic commented, approaching his sister while carrying some small spheres that sizzled faintly. “What is it and who got this?”

The little fox glowed with pride as he recognized them, running towards Manic.

“I built them myself.” Said the little guy with complete confidence. “They are useful to inhibit the robots and their effect lasts for ten minutes so we should have more than enough time to get out of here without them noticing.”

“You...you built them? Dude why haven't we heard from you? This is awesome!” Manic complimented. The little guy blushed and rubbed his nose with one finger. Sonia smiled at the gesture.

“Congratulations little guy, you've been quite a hero.” Sonia praised him. The little fox seemed to want to say something else, but she knew they weren't sure yet. The tyrant's surveillance system would soon notice the SAWTBots' casualty. “So...why don't we just take them home?”

The younger boy shook his head. 

“I live a block away so I can be there in a moment. Still, I appreciate it.”

Manic didn't agree so much. “Are you sure, kid?” And the little mobian nodded. With a place in mind the little guy started to walk. “Again. Thank you very much... uh…”

“Tails. Call me Tails.” The smaller mobian smiled and nodded in delight.

“Thanks Tails!” And he ran off.

“What about you? Do you live nearby?” Manic asked the remaining little fox.

“Uh... I…” Tails came out to the roadside, looking around. His face showed concern, and the little twitch of scratching his cheek confirmed it.  “I'm sure I don't live around here?” he said, turning to the hedgehogs. “Where are we?

The brothers raised an eyebrow.

Manic sighed. “Don't you know Robotropolis?”

“Robo... what?”

Before they could answer, sirens began to sound nearby.

“Tsk, troubles…” Sonia announced with total displeasure.

“It's time to go guys.” Manic said, getting on his hoverboard. “Those things are really annoying.”

Sonia nodded, then looked at Tails for a moment. She wasn't entirely sure why, but something told her this little guy would be important. “Why don't you join us? I'm sure you'll love talking to Cyrus.”

Manic looked at her suspiciously. It didn't seem like a good time to bring more people into the little “lair” where they were hiding, but she didn't say anything. She decided to trust her sister's intuition.

Tails took one last look around before deciding. “I think that would be better than being stranded here.”

And with that answer, Sonia helped Tails get on the pink motorcycle.

“Lead the way, Manic!” Sonia asked while the engine of her motorcycle roared. Manic accepted the request and started the escape route.

Sonia followed close behind.

They had not gone far when two red scorpion-shaped ships appeared, trying to shoot them down. Both siblings managed to dodge them.

“PRIORITY NUMBER ONE. ERIZOS” It was heard over the loudspeakers. “SURRENDER.”

Tails watched as several humanoid robotic units descended from the ships and began firing lasers at them. The situation seemed eerily familiar.

“Why are they after us?”

“For doing the same thing you did back there,” Sonia replied as she dodged a laser. “Being defenders of freedom.”

Tails frowned. The situation seemed very similar to his day to day life. But not at all they had metallic buildings, dirty streets and not even a smoggy sky and air, this brought back some memories to Tails from “Chemical Plant Zone” of a certain recurring enemy. And like a puzzle, the situation began to take shape for him.

“Wait a second, Eggman's behind this?!” Tails' alarms went off.

“Eggman? Ha!” laughed Manic as he did a somersault in the air. “Why haven't we ever called him that, Sonia? The old man is clearly shaped like an egg!”

“Manic, look straight ahead!” Sonia scolded. A pair of SAWTBots brushed past him. Fortunately, Manic managed to dodge them in time: “They're giving me spikes!”

“Tails!” Manic called to a distracted little fox. “Do you think maybe we can use one of those little balls of yours, buddy?”

“The Pinball Shock?” 

“That's a good name.” Sonia praised and then dodged three more lasers that passed close by.

“Ehhh... I've only got one more shock left. But they have to be together if we want to lose them all.”

“Then let Manic set the trap while we serve as bait,” Sonia decided. Manic hesitated as he broke away, but when he saw a new squad of SAWTBots approaching, he nodded. Tails tossed him a baggie and Manic caught it before taking another route.

“Good luck!” he shouted as he was lost in the smoke from the strainers.

Sonia roared with the engine and turned down the next street, attracting the enemies.

“How will Manic know where to meet them?” Tails asked.

“We've been fighting together for years. We understand each other with a look.” Sonia said with her eyes straight ahead. She took the next junction and in the next burst of lasers used large structures as protection.

Tails didn't like what he heard. “How long have they been battling Eggman?”

“Against Buttnik? The bastard's been ruling Mobius for over a decade.” Tails frowned even more: “Once we knew how to take a weapon, we didn't hesitate to join the resistance.” Sonia added, noticing the confusion on his face. “How did you get to Robotropolis? Don't you know there are better places to go sightseeing?”

The hedgehog laughed softly, trying to lighten the boy's weight as he took another route with the robots at his heels.

Tails laughed weakly.

“I... I don't quite remember how I got here…” Tails actively searched his thoughts, but try as he might, there seemed to be a big haze “I think the last thing I remember is that I was with Sonic and....”

“So-sonic?” Sonia tensed when she heard the name.

“Have you seen him?”

“I... uh... No... well... I…” The stammering in the girl increased noticeably which alarmed Tails.

“Sonia... Are you okay?”

But she stopped paying attention. Her mind seemed to be plunged in darkness, and her body barely reacted. The bike began to lose speed, the zigzags less precise, until....

“Sonia, look out!”

Tails reacted, grabbed her by the shoulders and jumped off the bike just before impact.

The sudden jerk made Sonia react and the realization of what had just happened made her prepare for the worst. And when she noticed that nothing had happened yet, she was surprised to see her feet dangling in the air. As she searched for an explanation for this, she could only observe the little fox concentrating on staying in the air.

“Can you fly!”

Tails smiled without missing a beat. 

“It's thanks to my two tails!” he announced proudly in the air.

“Is that why your name is Tails?” Tails smiled and nodded. He was about to say more, but held back. Sonia noticed the gesture. “Boy, I'm sorry, I... I don't know what came over me...”

“Don't worry about it. Shall I go? Just tell me which direction to take.”

Sonia smiled gratefully and tried to focus again. “Keep up that pace in the same direction, while I'll try to take down the enemy!” Tails nodded. Sonia activated the medallion on her neck, which transformed into a keyboard-shaped weapon, ideal for her size.

With the new offensive attack, the ships and robots began to dodge the lasers, but without stopping attacking. At first she managed to shoot down four flying combat robots but in a short time they were joined by four more.

During the battle Sonia couldn't help but notice Tails' bravery and the firm way he held her. As if it wasn't the first time he had flown with someone. More surprising, was the fact that he could keep the speed he was carrying, matching that of his bike, even Sonia dared to think that the boy could keep up with his brother in blue... 

“Sonia, which way should I go?”

announced the little fox as three different streets loomed.

“Last one on the left!”

Tails agreed and took the said course.

Tails obeyed. They advanced through the streets, but Sonia noticed a tremor in the boy's hands.

“Is everything all right?” And when she saw his face, she noticed the tiredness in the other one. They had to stop but... They could not. They would be finished if they did.

“D-don't worry... uff... just... I-I'm still straight right?”

Sonia nodded worriedly. Not wanting to overstrain him but she had to encourage him for a little longer. “We're only a couple of blocks away from meeting up with Manic.”

Tails felt his hands burning, but he didn't stop. He understood the gravity of the moment. So he kept zigzagging, dodging, using structures around him to reduce the direct effort.

Everything was going well... until he passed by a streetlight that suddenly exploded, hit by a green laser. The shockwave hit him squarely, knocking him off balance.

They both fell sharply to the asphalt.

The impact was strong enough to stun them. The seconds that followed were enough for the enemies to close in and surround them.

“PRIORITY NUMBER ONE. ENEMY OF THE STATE.” announced the robots, aiming at them without hesitation.

Out of pure instinct, Sonia got up as fast as she could to cover Tails, but as soon as she took a step, a pair of large metallic hands, tinged with purple, caught her completely.

“Sonia! Hey!” Tails tried to imitate her, but ended up the same way: suspended in the air, held by her two tails. “Leave us alone!”

Sonia felt completely vulnerable.

Panic invaded her chest like a cold wave, paralyzing her. She knew it was absurd to stay still, that she should fight or do something, but her body did not respond. Her mind, trapped in a spiral, began to drag her back to memories of the day when everything changed. The day the resistance lost its way. The day when...

“Hey, let go immediately!”

Sonia didn't remember closing her eyes. But at the sound of that familiar, youthful voice, she snapped them open.

And in a breath - or rather, a gust of wind - she found herself sitting on the floor, free from the grip of the machines.

It all happened so fast she could barely process it. She heard only laser shots... muffled by several consecutive explosions.

“Sonic!” Tails exclaimed, with a joy so vivid, so hopeful, that Sonia felt her heart flutter with relief.

The little fox ran straight to the figure of the blue hedgehog, who was already a few steps away from them, smiling from ear to ear. He greeted him with a warm hug, while behind him lay the smoldering remains of the squadron of SAWTBots and the fighter ships that had been chasing them.

“Tails! I'm glad I found you,” said Sonic, leaving the embrace for a moment to take the little guy by the shoulders and inspect him. “Are you all right?”

“Just a few minor scrapes,” replied Tails, pointing to the affected areas.

“What about your tails?”

Tails wagged them slightly and shook his head.

“A little sore from the rough grip, but all good.” He assured him. Then she looked at him with relief. “For a moment I thought we weren't counting.”

“You should know that I cause the problems, not you, little guy.” Sonic replied with a smile, causing them both to laugh.

“I wanted to experience what you always do.”

“Well, next time, make sure you come out unscathed.” Sonic winked.

“I've got it in mind.” Tails joked, and they laughed together again.

Sonic couldn't help but ruffle his fur affectionately.

The atmosphere felt light. Very different from the tension of just a few minutes ago.

“Sonic?” the blue hedgehog turned at the call.

“Sonic?" a female voice called, and the blue hedgehog turned around.

“Uh, Tails... You haven't introduced me to your friend yet.” he commented, looking at the hedgehog. Sonia barely frowned her right eyelid.

“Right! Sonic, this is Sonia.” Tails said, approaching her to help her up. “She's a freedom fighter. And you should also meet her brother. His name is Manic, by the way, he…?”

“Stop your tails for a second.” Sonic interrupted, frowning.  “Defenders of freedom, you say? What does that mean?”

“Well, it seems we're in a place ruled by Eggman, and from what I understand…”

“Seems?” Sonia interjected, with an incredulous laugh that was choked with anger. “As much as I would love for this to be a dream, unfortunately we live under Robotnik's tyranny. And it's only going to get worse since you...!”

“Are you guys all right?!” Manic's voice broke in as he came speeding in, parking near his sister. “I heard explosions and assumed it was you guys because I didn't see you nearby. So I came as fast... as... as... I... could…” Manic slowed his concern as he saw the blue hedgehog in front of them. “Unkempt hedgehogs... Is it true what my eyes see?”

“Definitely a Robotnik trick,” grunted Sonia, recovering from the shock before her brother. Without thinking twice, she activated her medallion. This alarmed Tails, while Manic stood on the sidelines, clearly waiting for an explanation. “It may look like him but I know it's not him.”  Sonia said, in an icy tone.

From his place, the green hedgehog inspected Sonic carefully. Not once, not twice... but three times.

Sonic, for his part, ignored the distressed way Manic was watching him. He simply crossed his arms, unfazed by the cautious attitude of both hedgehogs.

“Well, maybe he's missing a few pounds of chillidogs on him and he looks taller but…” Manic cocked his head to one side as he watched. Sonic lowered his ears, offended, and Tails raised an eyebrow. “...I don't see that much of a problem from there. Maybe Robuttnik left him without food? Wait, Sonic had green eyes?” That last detail completely changed Manic's countenance.

“Sonia, what's going on?” asked Tails, in a slow voice, noticing the girl's growing hostility.

“We know Sonic perfectly well. And him.” Sonia pointed out firmly. “He's not the hedgehog he claims to be.”

“Pfff!...” Sonic let out a stifled laugh. “Me??????”

“Well, he looks like the same old same old to me…” Tails looked at him carefully, trying to see what Sonia claimed so confidently.

“And to me, a complete impostor!” said Sonia.

“Is it really necessary to say that?” Sonic complained, raising his arms in the air. He took a step, but Sonia raised her gun, stopping him in his tracks. He sighed, resigned, and remained in place. “If I had a nickel for all the times I've been called that, I'd probably have enough for a ChilliDog by now.”

“Hey. I don't know what happened here, but I know Sonic perfectly well.” Said Tails, positioning himself between the two sides. “And I don't think it's fair how they're treating him... especially when he just saved our asses.”

Manic noticed the confidence in the boy's voice. It stole a small smile from him... which faded as soon as he looked back at the blue hedgehog. His face reflected the same thing as his sister's: conflict. And he didn't blame her. He understood what she was feeling.

“You seem to know him well friend” he said at last, in a softer voice. Deep down, Manic wanted hope. He wished that clinging to her wouldn't end badly. “How come you're so sure?”

Tails glowed as he looked at the blue hedgehog. “More than my friend, he's my big brother. Impossible for me not to know him.”

Sonia and Manic took time to digest those words. They were full of conviction. The pain in their chests seemed to fit better as they watched Sonic smile proudly at Tails.

The brotherly look the two shared was the bitter icing on their cake of woe. Impossible for something like that to be a lie.

Sonia simply deactivated her weapon.

She couldn't fight it.

In the distance, new police sirens sounded again.

The royal siblings shared another conflicted look. Sonia refused to accept what was happening, while Manic couldn't help but feel intrigued by the whole mysterious situation.

Sonia knew she shared the same curiosity. Or maybe… she just wanted to cling to a lie. She didn't know. She sighed, defeated. "Tell Cyrus we're bringing company." Manic smiled at her sympathetically.

“I'll no longer have any way to justify ignoring…” And Manic readjusted himself on his board.

"Are you taking us with you?" Sonic asked, still confused by the sudden change. The nervous twitch in his foot became visible. The brothers noticed it: such a small, spontaneous detail… it seemed impossible for someone like Robotnik to replicate. "So what happened to all the hostility?" Sonic added, frowning.

"I don't want you to expose Tails to danger," Sonia replied as she headed toward her brother's hoverboard. "or the robotizer…" Sonic didn't respond to that, but he hated the implication.

“Tails, can you still fly?” he asked softly. The little fox looked at his tails doubtfully, which made his brother’s decision easier. “Then it’ll be the old-fashioned way.” Tails smiled, embarrassed… but also excited. He’d never admit it out loud, but he missed riding piggyback. Sonic, now with a plan in mind, approached the royal siblings. “We’ll follow on foot.”

The scruffy-spined hedgehog raised his thumb in recognition, and together with his sister they began to surf the air.

Notes:

The upload schedule will be approximately monthly. (But it could take a little longer, depending on the complexity.)

Don't forget to give a kuddo up if you like the story, and comments are free :3 (They might even speed up the upload of chapters 👀🔥)