YOUR HEART GOT TEETH
Jack Spicer x OC

When a fearsome killer sent by Chase Young arrives at Jack Spicer's lair to eliminate him, their battle ends with her at Jack's by her strength and resilience, Jack spares her life, leading to an unlikely alliance. (aka, Jack Spicer stars in "How to Train Your Monster Girl")

Set a couple years after the end of Xiaolin Showdown!

CHAPTER 1: THE WOLF AT YOUR DOOR

Jack Spicer's lair was an explosion waiting to happen.

Not literally — at least, not yet — but it had all the chaotic energy of one. The place was a sprawling mess of half-built robots, blueprints strewn across tables, and the faint hum of circuitry that filled the air like the buzz of a thousand mosquitoes. Tools and wires lay tangled underfoot, ready to trip up anyone stupid enough to walk through without a strategy. Jack's strategy? Ignore it.

He sat hunched over a control panel, bathed in the cold blue glow of half a dozen monitors. His goggles perched on top of his head like a mad scientist's crown, and he was giving his latest creation the kind of look that said, Oh yeah, this is gonna be awesome .

"This time," Jack muttered, soldering iron in hand, "this time, those monks won't know what hit them. I'm talking full-on destruction. They'll be begging for mercy before I'm done!" He barked a laugh, tossing the tool aside and swiveling to face one of his robots. "What do you think? Too much?"

The robot's lifeless red eyes blinked back at him.

"I know, right?" Jack leaned back in his chair, grinning like he'd just won an award for 'World's Most Evil Genius.' "I mean, Chase Young might think he's all high and mighty, with his ancient powers and cat warriors, but I've got technology. Robots. And everyone knows tech beats brawn every time."

He tossed a crumpled blueprint over his shoulder, already imagining the headlines: Jack Spicer, Boy Genius, Outsmarts All! Chase Who?

What he didn't imagine was the danger creeping into his lair, silent as a shadow and twice as deadly.

From the farthest corner of the lair, near the grated ceiling vent, something moved — a dark, slithering figure blending seamlessly with the clutter. Crimson eyes gleamed in the dim light, locked onto her target with predatory precision. Her muscles coiled beneath her skin, taut and ready, but for now, she stayed hidden, watching. Calculating.

Her claws flexed against the cold metal floor, the soft scrape drowned out by Jack's own voice as he ranted to an audience of unblinking robots.

"You know, they never give me credit for the real genius I am!" Jack's arms flew wide, almost knocking over a tool kit. "I bet right now Chase is sitting in his lair, brooding like a wannabe Bond villain, thinking he's all that because of some mystical mumbo jumbo. But me? I've got brains. I've got—"

A clang echoed from the far end of the lair.

Jack froze, mid-gloat. His goggles slid down over his eyes, and he reached up to adjust them with a snap. "Uh… hello?"

Silence.

He peered around, squinting into the maze of wires and gears, but saw nothing. His bravado kicked in a second later. "Psh, must be the new bots moving around. No big deal. Probably just testing themselves! Brilliant, right?" He chuckled nervously and went back to fiddling with his invention.

But she was still there, a dark blur of movement that even Jack's sharp robots didn't detect. She circled him like a wolf hunting its prey, her every step measured, calculated. Her sharp gaze flickered with cold amusement. This was the one Chase had sent her after? This arrogant fool who couldn't even sense danger when it was breathing down his neck?

Pathetic .

Her muscles tensed. Soon, she'd strike. But for now, she waited. Let the fool think he was safe.

Jack leaned forward, cranking a few bolts. "Anyway, once I finish this baby, I'll be unstoppable! Chase will—"

The vent above him creaked. This time, Jack didn't miss it. His head jerked up, and his fingers hovered above the keyboard, eyes darting toward the noise.

"Okay, that wasn't the bots," he muttered. "Who's there?"

Still, nothing. The lair was as quiet as ever, save for the hum of Jack's monitors. But now his confidence was crumbling around the edges. Jack was good at a lot of things, but listening wasn't one of them. He wasn't great at picking up on ominous warnings either.

A low growl came from somewhere in the shadows.

That, Jack couldn't ignore. His heart raced. "Whoever you are, I have robots ! Big ones! And I'm not afraid to—"

Crash!

Before he could finish, a shadow launched itself from the rafters above, a blur of black and white crashing down onto the floor with a feral snarl. Jack barely had time to react before she pounced, her claws slashing through the air.

Jack yelped and scrambled backward, nearly tripping over his chair. "What the—?!"

Her eyes burned like embers, a deadly calm in her stance as she stalked toward him, her reptilian tail swishing low to the ground. Jack's cocky smirk was long gone, replaced with wide-eyed panic.

"Oh, come on!" Jack squeaked, frantically reaching for his controls. "I don't even know you!"

She growled, baring her sharp teeth. "You will now."

The mysterious predator took a slow, measured step forward, emerging from the shadows. Now, in the dim light of the lair, Jack could finally get a good look at her, and for a split second, his bravado flickered. He stared at the figure in front of him, blinking several times as if that might make her disappear.

Her short black fell in jagged layers, with snow white bangs that framed her face. Blood red eyes, sharp as a blade, gleamed with an almost predatory hunger. Her lips curved into a smirk, revealing sharp teeth that could probably tear through metal like butter. Her lethal claws clicked softly as she flexed her fingers, and the talons on her raptor-like feet left deep scratches in the floor with each step. A long black reptilian tail swished behind her, moving with the same fluid grace as the rest of her lithe, powerful form. Black tribal markings ran down her jawline, a stark contrast against her pale skin like war paint.

She was standing tall — well, not that tall — right in the middle of his lair like she owned the place, a swirling presence of black and white. Her eyes were locked on him with the cold precision of a sniper. There was something distinctly inhuman about her movements, every slight shift of her body graceful and deliberate, like a panther stalking through tall grass.

"Okay, seriously, who are you?" Jack asked, pushing himself to his feet with more bravado than he felt, and pointed a shaky finger at her. "Because I wasn't expecting visitors today, and I'm kind of in the middle of—"

"I'm here to kill you," She spoke flatly, her voice low and unbothered, as if she were mentioning the weather.

Jack blinked again. "Wait, what?"

She took a step forward, her sharp claws clicking with each step. Her gaze never wavered, watching him with the focus of a predator who already knew the outcome of the hunt. "Chase Young sends his regards."

"Ohhhh," Jack said, recognition dawning. He rubbed his chin, eyebrows raising in mock understanding. "Chase, huh? Yeah, should've known. He loves sending random minions after me. Not that I blame him. I am his greatest rival, after all."

She just stared at him.

Jack gestured toward her vaguely, trying to keep up the cocky façade. "You must be, uh, new around here. Usually, he sends giant jungle cats or something, but I guess you're supposed to be… what, his latest upgrade? A custom model?"

She said nothing, but the corner of her mouth twitched in the faintest hint of a smirk.

Jack paced a bit, shaking his head as if amused by the absurdity of it all. "Well, I hate to break it to you, but Chase has seriously underestimated my genius. I mean, look around." He spread his arms wide to indicate the lair, the dozens of Jack-Bots stationed in the shadows, the workbench cluttered with half-finished inventions. "This is my turf. You're outmatched, outclassed, and — no offense — you're not the first freaky thing that's tried to kill me."

Her expression didn't change. If anything, she seemed even more bored.

"Look, let's skip the whole 'fight to the death' thing," Jack said, waving a hand dismissively. "I'll just send you back to Chase with a cute little 'sorry for your loss' card, and we can all pretend this never happened. Sound good?"

Her claws flexed, her tail swishing once, twice, before curling behind her. "No."

Jack's smile faltered for a split second, but he quickly recovered, turning toward his control panel. "All right, don't say I didn't warn you!"

He slammed his hand onto a large red button, and immediately, several Jack-Bots roared to life, their eyes glowing red as they turned toward her. Their metallic bodies clanked forward, their arms raised, and a series of laser pointers zeroed in on her. Jack grinned smugly. "Get her, boys!"

The bots charged.

For a moment, she didn't move. She just stood there, letting the chaos come to her. But then, in a sudden blur of black and white, she was in motion.

Her first attack was vicious, swift, and precise. In one fluid motion, she leaped into the air, her talon-like feet finding the first Jack-Bot's head with terrifying accuracy. A quick slash of her claws, and sparks flew as the bot's head came clean off, bouncing across the floor with a hollow clank.

Jack's jaw dropped. "Whoa, okay, that was… unexpected."

But before he could command the rest of his robots, she had already ripped through another two, her claws slashing with surgical precision. The bots barely had time to fire their lasers before they were reduced to scrap metal. One bot lunged at her with its heavy arms, but she sidestepped it effortlessly, sliding her tail under its legs and sending it crashing into the wall with a deafening clash of metal on metal.

Jack's fingers hovered above his control panel as he watched, wide-eyed and slack-jawed. "Uhh… guys? A little help here?!"

The remaining Jack-Bots regrouped, their movements jerky as they tried to surround her. One fired a barrage of energy blasts at her, but she darted across the floor, dodging them with serpent-like fluidity. In a flash, she was on top of it, slamming her fist down onto the bot's central core with a sickening crunch. The bot shuddered and crumpled to the ground, sparks fizzling out from its chest.

Jack threw his hands up. "Come on!"

He frantically mashed the buttons on his control panel, summoning more Jack-Bots to the fray. They descended from the rafters, swarming toward her with a flurry of mechanical whirs and clicks.

"Yeah, see?" Jack said, his voice rising with nervous energy. "Now you're in trouble. This is, like, peak evil genius stuff right here. You can't possibly—"

She didn't even give him time to finish his sentence. She vaulted herself onto the nearest Jack-Bot, using it as a springboard to leap across the room, her claws digging into the next wave of bots before they could even raise their arms. Her movements were a blur — ruthless, efficient, and almost too fast to follow. Every strike was a death sentence for one of Jack's creations.

In less than a minute, the lair was littered with the remains of Jack-Bots, their twisted metal bodies sparking and sputtering on the floor. The battle had barely started, and she already stood victorious, her crimson gaze gleaming in the flickering light of Jack's destroyed machines.

He stood frozen, staring at the carnage in disbelief.

"Okay," he said, his voice an octave higher than usual. "That was… impressive."

She cracked her neck and stretched her claws, not even slightly winded. "Is that all?"

"Is that—" Jack sputtered, glancing from the wreckage to the creature in front of him. "No, that is not all! I have more robots! Stronger ones! And— and traps! And…"

She took a step forward, her gaze unwavering. She didn't need to say anything. The message was clear: she was far from done. And Jack? He was running out of ideas.

Jack scrambled to his feet, heart pounding. Her claws had left deep gouges in the metal workbench, and the sight of her eyes — cold, calculating, but now gleaming with a fiery anger — made the hairs on the back of his neck stand up. He backed away, frantically tapping at his wrist controller.

"Alright, time for a little… upgrade!" Jack declared, voice shaking only slightly. With a dramatic flourish, he pressed the big red button. The floor rumbled as panels slid open, revealing a new wave of Jack-Bots — sleek, taller, and bristling with advanced weaponry. These weren't his usual disposable models. No, these were the heavy-duty, don't-mess-with-me versions.

"Say hello to my Mega-Bots!" Jack announced, his voice edging back into its usual cocky tone. "They're bigger, stronger, and about a thousand times smarter than those tin cans you just shredded! You're toast."

She cocked her head, predatory eyes flicking over the new arrivals. The Mega-Bots towered over her, their metallic limbs gleaming, laser cannons aimed directly at her chest. But instead of faltering, her lips curved into a wry smirk.

"Ooh, more toys," she muttered, her voice laced with irritation.

Jack swallowed. "Okay, okay— this time for real. Mega-Bots, ATTACK!"

The robots surged forward, their cannons firing in unison. Red beams of energy shot through the air, illuminating the lair in a deadly light show. She moved like a shadow, weaving between the blasts with impossible agility. She leaped onto the nearest Mega-Bot, claws sinking into its metal shell as she yanked with brute force. Sparks flew, and the bot's arm tore free with a screech of twisting metal.

"Whoa, whoa, whoa— okay, that's new!" Jack yelped, taking a step back as she hurled the robot's arm like a battering ram into another approaching bot.

But these were tougher than the previous batch. Another Mega-Bot grabbed her from behind, its hydraulic fingers squeezing around her frame with crushing force. She let out a growl, spinning and slicing through its arm with her claws, but not before the bot's grip left a deep bruise along her ribs. She winced, pain flashing across her face for the first time.

Jack's smirk returned, though it was tinged with nervous energy. "See? Not so invincible now, are ya?"

She glared at him, her eyes blazing with fury, but she didn't stop. If anything, the pain seemed to fuel her rage. She launched herself at the next bot, claws flashing as she ripped into it, her tail lashing out like a whip, smashing into another.

Jack watched in awe — and a little bit of horror. This girl — no, this beast — was something else. No matter how hard his bots hit her, no matter how many injuries she took, she kept going, like some kind of nightmare that just wouldn't stop. Her movements were sharper now, driven by raw anger. The grace and precision were still there, but they were laced with something more primal, more savage.

Another bot landed a solid hit, its cannon catching her in the shoulder. She staggered, snarling, but before Jack could even celebrate, she was back on her feet, tearing through the bot like it was made of paper. Her claws raked across its chest, ripping through wires and circuits, and the bot collapsed in a heap of sparking debris.

"Seriously?!" Jack's voice was high-pitched now, a mix of disbelief and panic. "I just built those!"

She didn't respond. She was panting, blood dripping from a gash across her cheek, but her eyes were locked on him, and Jack could see it in her gaze. She was furious — and she was coming for him next.

"Okay, okay, think, Jack," he muttered, backing up slowly. "You've survived warriors, dragons, monks — you can handle one angry monster girl, right?"

She moved with terrifying speed, closing the distance between them in seconds. Jack barely had time to dodge as her claws sliced through the air where his head had been moments before. He stumbled, tripping over a stray wire, and hit the floor with a grunt.

She loomed over him, her breath ragged, blood and sweat dripping from her brow. Jack scrambled backward, his mind racing. He needed a plan — fast .

"Hey, let's talk about this!" Jack pleaded, holding up his hands in surrender. "You don't really want to kill me, right? I mean, I'm sure Chase would—"

"Shut up," she growled. Her voice was low, dangerous.

She lunged again, and this time, Jack barely managed to roll out of the way. He was running out of room to maneuver. His lair was falling apart around him, his precious robots reduced to scrap metal, and this girl — this monster — was about to end him.

For the first time in a long time, Jack Spicer felt real fear.

His breaths came in quick gasps as he scrambled to his feet, eyes darting around his wrecked lair. The room was filled with the wreckage of his prized robots, their twisted, sparking bodies strewn across the floor. And in the middle of it all stood the fierce she-beast — bleeding, panting, but still standing.

Her crimson eyes locked onto him, dark and feral, despite the blood trickling from the gashes on her body. Her stance was wobbly now, less graceful, but the unrelenting fury in her gaze hadn't wavered. She was a predator with one last strike in her.

Jack wiped the sweat from his brow, forcing a shaky smile. "You've, uh, had enough yet?" he called out, his voice cracking with forced confidence. He reached for his wrist controller again, hands trembling.

She didn't respond. Her chest heaved, each breath a struggle, but she refused to back down. Her claws glistened under the flickering lights, poised for another attack.

"Alright, no more Mr. Nice Jack," he muttered under his breath, fingers flying across the controls. His voice carried none of the bravado it once had. This time, he wasn't boasting. This was survival.

A low rumble echoed through the lair as one of his final traps activated — a massive, reinforced bot, twice the size of the others, its chest glowing with raw energy. Jack had been saving it for emergencies.

Apparently, this counted.

With a high-pitched whine, the bot released a pulse of electricity that crackled through the air, lighting up the entire lair in a brilliant, blinding flash. Her body stiffened as the wave of energy hit her, her muscles locking in place. Her growl turned into a choked gasp, and her claws twitched, trying and failing to swipe.

Jack winced as the bot delivered its final blow — a concussive blast that sent her flying backward. She hit the ground hard, skidding across the metal floor, her body tumbling like a ragdoll. The impact echoed through the room, and for a long moment, everything was still.

Jack lowered his wrist controller, heart hammering in his chest. "Whoa," he whispered. "Okay… okay, that worked."

But the tension didn't leave his shoulders. Slowly, he crept closer, eyes locked on the motionless form sprawled on the floor. She lay in a twisted heap, her black and white hair plastered to her bloodied face. Her limbs were bent at awkward angles, her tail limp behind her. She wasn't dead — he could see the faint rise and fall of her chest, shallow but steady.

Jack crouched down, hesitating, his hand hovering over one of his remaining bots. He could end it right now, finish her off while she was defenseless. A part of him — the part that had been terrified for the last few minutes — screamed at him to do it.

But another part… didn't.

He stared at her, taking in the extent of the damage she'd taken. No one — no thing — should've been able to survive that much punishment. And yet, here she was, bloodied and battered but still breathing. The sheer strength it must've taken to keep going, the tenacity — it was impressive. Against his better judgment, Jack found himself… intrigued.

"Huh." He rubbed his chin, glancing down at the unconscious form before him. "You're a tough one, aren't you?"

She didn't respond, obviously, but the silence that followed was deafening. Jack stood over her, a strange conflict brewing in his chest. Chase had sent her to kill him. That much was clear. And yet, the longer he stared at her, the less he wanted to finish her off.

"Maybe we can work something out," Jack murmured, more to himself than to her. He knelt down, cautiously pressing his fingers to the side of her neck. Her pulse was weak, but it was there. He grimaced at the blood pooling beneath her, the deep gashes in her skin.

"Yeah, you're not getting up anytime soon," he said, frowning. "Which means I'm stuck with you."

Slowly, Jack stood, glancing around the wreckage of his lair. What was he supposed to do now? He couldn't exactly let her go. She'd probably tear him apart the moment she woke up. But… killing her? No, no, that didn't feel right. There was something about her — something fierce, dangerous, but also… vulnerable. Chase had sent her after him like she was just another weapon. Maybe, just maybe, there was more to her than that.

Jack crossed his arms, pacing back and forth. "Alright, think. You've got a super-powerful assassin here. She's injured, totally at your mercy. Chase wants you dead, but she didn't finish the job. So… what do you do?"

He stopped, glancing back at her. Her face was still, her expression peaceful despite the blood smeared across her cheeks. His chest tightened.

"I patch her up, that's what," Jack muttered, reaching for a nearby toolkit. "And maybe — just maybe — she and I can come to some kind of… agreement."

With one last cautious glance at her, Jack began gathering supplies, preparing to tend to her wounds. He didn't know what he was getting himself into, but one thing was certain — this predator-prey dynamic was shifting into something more complicated. Something dangerous.

But Jack Spicer, evil genius, was all in.