A/N: a non-canon interlude of Mako-humans inspired by a comment by kitsunesongs on AO3, exploring what would happen if a canon, post AC Cloud time travelled back to the past and met little gremlin Mako-humans Sephiroth instead.

Sephiroth was practicing the trombone when Cloud burst into the secure specimen containment cell.

Cloud paused on the threshold, bewildered.

Sephiroth's playing trailed off with a downwards descending noise, like a comically sad sound effect.

Cloud looked at the eight year old version of his enemy, holding a trombone. The tiny Sephiroth looked back. Behind him, the room was piled high with instruments and instrument cases.

The little Sephiroth lowered his trombone and looked at Cloud with huge eyes. They were wide and innocent, yet still that shade of familiar piercing green. A look of concentrated effort was on his face, and Cloud could almost see the cogs turning in that little silver head.

Was... Was Hojo locking Sephiroth up in a cell to make him focus on music practice?! Talk about an overbearing parent.

Sephiroth's lips trembled. Cloud's heart sank.The little kid looked so bewildered, and his hair was sticking up in a child's clumsy approximation of a bun. He was also wearing a paper gown, chocobo print boxers, and a pair of ugly flip flops with a big sparkly S made of glittery hot glue affixed to each of the straps. He was covered head to toe in cuts and bruises and currently sporting an IV line pumping him full of mako, which he didn't seem to even be noticing. Cloud stepped forwards and moved almost without conscious thought.

"Should you be playing the trombone with that in your arm?" Cloud demanded, sweeping into the room and pulling the kid's hand into his own to examine it. It seemed to be fine, but Cloud wasn't sure if it really was fine, or if Sephiroth just healed too fast for any marks to show.

After the catheter had been checked and the overwhelming parental urge satisfied, Cloud realised what he had done and froze. He wasn't supposed to be checking his enemy for little boo-boos! He was here to kill the man! After taking care of Jenova and the majority of Shinra's mako reactors, Cloud had made his way to Midgar and torn through Shinra's Executive Board and Science Department like they were so much tissue paper. He only needed to take care of Sephiroth to ensure that the desolation of the future would not come to pass.

"I- um," the little Sephiroth said timidly, tugging on a stray strand of his long silver hair. He looked up hopefully at Cloud. "Are you here to let me out of my cell?" He asked in a quavering, tremulous voice.

"H-hello," Cloud said awkwardly. He attempted to hide the bloody Fusion Sword he was holding behind his back. "I- yes. Yes I am."

A smile broke over the kid's face. "I promise I won't make a racket in public anymore," he said earnestly. He set his trombone down on top of its case and grabbed his IV stand with a thoughtless movement that spoke of long practice, then looked hopefully between Cloud and the door.

It was a heavy steel door with a one way observation window, and the cramped room it guarded was a windowless cell with a toilet and a sink and a barren, unpadded wooden plank for a bed. The only other furniture was the swivelling dentist's stool that served as the piano bench, and a music stand. The lights hadn't even been on when Cloud had burst in. Cloud desperately hoped that Sephiroth didn't sleep here.

Cloud couldn't imagine what it would be like, tooting away like nothing was wrong in a pitch black room while actively receiving a mako infusion. No wonder the kid would grow up funny in the head. The fact that this little Sephiroth wasn't a whiny, sobbing mess while he had the mako drip in, but was going about his daily tasks and not even showing any sign of pain was horrifying enough. But maybe it was just that a treasured asset like Sephiroth received treatments differently from disposable specimens like Cloud. Maybe his solution of mako did not feel like hot acid eating away at the insides like a million agitated fire ants.

"Hey, kid," Cloud said. "What's up with the mako? Doesn't it hurt?"

Little Sephiroth looked at the three bags of brightly glowing mako in confusion.

"Yes?" He said, looking anxious that he was giving the wrong answer. "I- I haven't developed an insensitivity, if that's what you mean. I'm having the same response to the infusion as always. Pain, nausea, light sensitivity, olfactory and tactile hallucinations, activation of the Reunion response in my transplanted organs, dryness of the eyes, minor bleeding of the gums, heart palpitations and sweating. I can't feel my bones trying to reject my implanted trackers, but Doctor Hojo said that that shouldn't be happening anymore after he replaced them with the new kind."

Cloud took a moment to process all of this. That was indeed the standard set of reactions to a mako infusion via IV, except the part with the trackers. Cloud hadn't had any under his skin while he underwent his procedures. Sephiroth seemed to grow even more nervous at Cloud's continuing silence.

"Oh no," he sighed, like something mild inconvenient had just occurred to him. "Am I going to have to get all of my implants replaced? Again? I have my martial arts assessments the day after tomorrow, my instructor are going to be so annoyed if I'm in too much pain to keep proper form."

Cloud grimaced at this. This was a lot more than he really wanted to know about the childhood his nemesis had once suffered. Was still suffering through.

Sephiroth awaited a response in anxious silence, alternately twisting a black choker necklace and a corded bracelet around his wrist. Cloud recognised the plain black bead on the choker and the nondescript metal closure of the bracelet as discreet tracking devices the Turks used to employ. He took several deliberate breathes through his nose, counting each one out. Why would a little kid in a cell need a tracking device?

Little Sephiroth wasn't unobservant. After a few wide eyed glances at Cloud, and at the bloody sword behind him, the kid blurted out, "Are you a SOLDIER? Are you here to assess my progress? I'm not sure I can give my best performance while in the middle of a course of mako. Could we wait until tomorrow? I promise I'm not trying to be difficult or disobedient, it's only that I don't think it would be am accurate assessment until after I can feel my legs again. SOLDIER Third Class Towers always says that I'm not good for much more than being a punching bag when we spar straight after a mako infusion."

Little Sephiroth kept looking to the side and down at his feet, but whenever he gathered up the courage to meet Cloud's eyes, his glowing cat-slit eyes would glisten with barely restrained tears. But he did his best to keep his wavering voice steady, and his trembling lips were rearranged into something that could almost be called a hopeful smile.

Cloud felt his resolve crumble into dust. He hadn't really thought he could kill a little kid anyway, but he'd at least thought he could fool himself for longer that this. Cloud returned his bloody sword to the harness on his back and bent down so that he was on the same level as Sephiroth.

"I'm not a SOLDIER," he said firmly. "I am not part of Shinra. I'm here to take you away."

Sephiroth flinched and hunched in on himself. "I- I shouldn't have told you about the trackers," he said, on the verge of tears. "I'm so stupid. The one thing Mr Veld always told me to never let a kidnapper know about was the trackers."

"No, Sephiroth," Cloud said. "I'm not a kidnapper. I just want to stop Hojo and Shinra from hurting you. Wouldn't you like to stop having mako infusions? Here, why don't you show me your hand and I can take that catheter out for you."

Sephiroth flinched again. "I'm not going to let you fool me," he said, bursting into tears. "It's my job to protect the company's research from theft. I won't let you take me or a sample of my mako infusion that easily. Besides, the Turks will come after me. Mr Veld promised. He won't let company assets be stolen like this. You can dissect me, but he won't let you live long enough to make any use of any data you gather from me."

Cloud swallowed down the urge to sigh. "Sephiroth. I am already enhanced. Look at the mako in my eyes. I don't need you for research. But wouldn't you like to go somewhere where you didn't have to be in pain all the time? Somewhere where you didn't get experimented on?"

Sephiroth looked up at Cloud, a look of childish incomprehension on his face. "I'm a Science specimen," he said. "It's my purpose to be experimented upon. That was what I was created for."

Cloud scowled fiercely, then gentled his expression.

"No, Sephiroth," he said. "You were born because your mother loved you and wanted you. That is all. She never wanted you to be mistreated like this."

Sephiroth tugged on a strand of his silver hair. "I... Doctor Hojo said-"

"Doctor Hojo will not be making any more decisions for you," Cloud said darkly. He paused, trying to get his temper under control. "I promise neither he nor anyone else in the science department will hurt you again."

Sephiroth stared at Cloud, then at the puddle of blood that had formed under the Fusion Sword. A look of realisation came upon his little pale face. Then his expression smoothed out into an unreadable wall of blankness.

"Did you kill him?" Sephiroth asked tonelessly.

Cloud hesitated, but Sephiroth wasn't an ordinary child. He couldn't justify lying to him.

"Yes," Cloud said.

Sephiroth mulled this over.

"What about the other scientists? Are they dead too?"

Cloud nodded wordlessly.

"And the president?" An expression was starting to emerge from that delicate little face, but Cloud couldn't quite work out what it was.

"And the president too," Cloud confirmed.

"And the research specimens?" Sephiroth's gaze intensified.

Cloud hesitated. "I- I destroyed the dangerous ones, but I haven't harmed any of the human specimens, I promise. I won't hurt you."

Sephiroth's face was ashen white, and he trembled slightly.

"And Jenova? What about Jenova?"

A cascade of ice ran down Cloud's spine.

"How do you know that name?" He growled, hand on the hilt of his sword. Perhaps this Sephiroth was not as much a child as he appeared. If Cloud had managed time travel, it was entirely likely that Sephiroth could have followed him.

"Please," the little boy said, trembling. "Have you destroyed her? I need to know. You can kill me afterwards if you like. I just have to-"

The kid's throat closed up around his words, and he wiped angrily at the tears on his face with the hem of his paper gown.

"Jenova has been destroyed," Cloud said coldly, steeling himself for an attempt at retribution.

Sephiroth collapsed to his knees instead. He didn't even seem to notice it, staring into the middle distance with a look of vague disbelief. After a brief moment of concentration, he covered his eyes with one hand and started to laugh.

"You did it!" Sephiroth sobbed. He was giggling and laughing. "All these years I waited and planned and bided my time and let Hojo treat me like a bug under a microscope, and you just..."

Sephiroth peeled away the tape holding in his catheter and pulled it out with a practiced, careless motion. A bead of glowing green liquid welled up after the needle, which sprayed the solution out and dripped the essence of the lifestream out onto the cold concrete floor.

Sephiroth was smiling manically, but it wasn't the same kind of crazed expression his adult counterpart used to wear. He held his arms up towards Cloud, in the universal gesture of a child who wanted to be picked up. He was really a little too big for it, but the tears streaming down his face and the look of frantic intensity in his eyes made Cloud disinclined to upset him. Cloud picked the boy up and propped him up on one hip. The boy clutched at Cloud's shoulder, still giggling and sobbing.

"Please," he said. "I gotta see. I have to make sure Hojo is... I have to know for certain."

It was the work of a moment to carry Sephiroth out of the cell and down the hallway, where Hojo had made his last stand with his gun in hand, convinced Cloud was trying to steal his research.

Sephiroth gasped when he saw the body and wriggled out of Cloud's hold. He leapt nimbly to the ground and sprinted towards Hojo's corpse, kneeling down and peering curiously at it, as if he was a regular little kid looking at a new and interesting bug he'd found.

Then Sephiroth stood up and gave Hojo's torso several vicious kicks.

"Experiment on this, you amoral sadistic motherfucking asshole! You stupid unethical hack!" Sephiroth howled. He emitted a screech of rage, tearing at the roots of his own hair. He held out his hand, and the shape of Masamune, too big for his tiny body, began to slowly and clumsily manifest. Sephiroth didn't seem to care that he was damaging the blade and scraping it against the wall as he hacked at Hojo with it, cursing like a seasoned sailor.

He was shuddering with the force of his sobs when he eventually stopped and threw Masamune aside like it was a no-longer-interesting toy. Cloud, who had stood back, stunned, unclenched his hand from the hilt of his sword. His Sephiroth had never treated Masamune like that. This little kid, whatever he was, whatever he knew, wasn't the same kind of consummate warrior as the Sephiroth Cloud had once known.

He approached the kid silently, and pressed a comforting hand to his shoulder. Sephiroth was still heaving with emotion and exertion. Eventually, he collected himself again, wiped off his tears, and stood with his eyes closed, focusing very hard inward. Cloud debated pulling the kid into a hug. He hoped this baby Sephiroth wasn't having a mental breakdown.

After a few dozen careful, measured meditative breaths from little Sephiroth, the kid opened his eyes and burst into a startling, hair-raising smile. He beamed at Cloud like a toddler who has just been given a whole bucket of candy. The anguish that had consumed him only a minute ago disappeared, the overwrought timidity that had greeted Cloud in that holding cell was nowhere to be found.

The smiley little kid bounced in place a little bit as he tugged on Cloud's sleeve and chirped, "Wow! Thanks for taking care of him, Cloud! That was so cool of you. Now I don't have to grow up to be a megacorporation-toppling parent-murdering terrorist mutant Dark Fuck Prince like I was planning to be! Say, can I be your sidekick? Have you visited Vincent yet? How about my mom? Lucrecia, I mean, not stupid Jenova and her stupid alien face. Have you been to see Aerith? She's such a cute baby! She's only two doors down from my music room, you know. Hey! Do you wanna meet Yuuki? He's my little brother. Well, more like a clone of me who was spliced with Vincent's DNA, but I like to think of him as my stupid baby brother. Oh yeah! Did anyone else time travel with you? Can I meet them? Please? Pretty please? Do you think you can also shank Hollander? But Genesis and Angeal might need him though. Ugh. But Ifalna and Aerith exist, maybe they could help! And I know a lot more about how Hojo is enhancing me than stupid stinky canon Sephiroth did in your timeline."

"Woah woah woah," Cloud said, putting his hands up. "What is going on here?"

Sephiroth looked up at him with a gap-toothed smile. "We're having a fun trope crossover, silly!" He chirped. "I've been transmigrated, you're a Peggy Sue. No better wish fulfilment that the two of us, baby!"

Cloud rubbed his throbbing temples.

"I have no idea what and or who those are," he said. "Are you or are you not Sephiroth from my timeline?"

"Nope!" Baby Sephiroth said. "I'm from a different dimension."

"And how do you know who I am?"

The little gremlin hummed in thought. "Do we have video games in this dimension yet?" He wondered. "I haven't really looked into it because early video game graphics suck and their sound design always give me a headache. Anyway, I know about you because of this fun hobby I used to have called speedrunning!"

The conversation started out making zero sense, and only went downhill from there.

When Cloud exited the Shinra Building hand in hand with little Sephiroth, he had a comatose Sephiroth clone named Yuuki slung over his shoulder and Ifalna holding following behind with Aerith in her arms. Veld was waiting to intercept them. Cloud paused, letting go of Sephiroth and preparing to set Yuuki down to fight the Turk.

"Wait," Sephiroth whispered. "Let me talk to him real quick."

Bemused, Cloud watched as Veld's jaw tighten and his forehead wrinkles deepen at the sight of little Sephiroth skipping up to him and bouncing up and down in front of him with a big beaming smile.

"Mr Veld!" Little Sephiroth said, "My mother has sent Cloud to make me no longer your problem!"

Veld looked at Cloud, nodded at him with respect, and lowered his weapon.

"Just like that?" Cloud said in disbelief.

"She has a higher claim on him than Shinra," said Veld. He stepped aside. "Tell Vincent I said hello," he added, and ruffled Sephiroth's hair fondly. Sephiroth pulled a childish face at Veld, then tugged Cloud away from the Shinra Building, leaving all the blood and flames and shrieking sirens behind them.

Faintly, Cloud's enhanced hearing caught Veld muttering under his breath, "Good fucking luck babysitting, chump."

A/N: Chapter title from a famous Japanese version of One Winged Angel misheard lyrics that misinterped "Estuans Interius Ira Vehementi" as "塩酸、シメジ、ひらめ、出目金" (hydrochloric acid, shimeji mushrooms, Japanese halibut, telescope goldfish)