A few days later, the move-in happened.

Scott’s mansion was massive — modern, luxurious, with huge bedrooms and a big open living area. Lydia was over the moon, practically glowing as she unpacked her things into Scott’s master suite. She and Scott had been inseparable since the dinner, stealing kisses in the kitchen, whispering sweet things, already acting like a married couple. Scott kept one hand on her waist or ass whenever he could, looking at her like she hung the moon.

Stiles’s room was right next door to Derek’s.

The second Scott showed her the room — big bed, walk-in closet, private bathroom, and only a thin wall separating her from Derek — Derek’s jaw tightened. He stood in the hallway with his arms crossed, tattoos flexing, watching them carry boxes in.

“Really, Dad?” he muttered under his breath when Scott stepped away. “Next to my room?”

Scott clapped him on the shoulder, smiling. “It’s the biggest guest room, son. She’s family now. You two are the same age — you’ll get along fine.”

Derek didn’t answer. He just glared at the closed door to Stiles’s new room and went back downstairs, already pissed. Living under the same roof with that fake-innocent little slut? Bad enough she was going to be his stepsister. Now he had to hear her moving around right next door every night?

Stiles, on the other hand, was thriving.

From day one she was a menace.

She wore the sluttiest clothes around the house — tiny crop tops that barely covered the bottom of her massive tits, micro shorts or tiny skirts that showed off her fat ass and long legs, sometimes just an oversized t-shirt with nothing underneath so her hard nipples poked through. Around Lydia she was still the sweet daughter — soft voice, helping in the kitchen, giggling at Scott’s jokes like an angel. But the second her mom’s back was turned, the real Stiles came out.

She flirted shamelessly with Derek.

Brushing past him in the hallway so her big tits pressed against his arm. Bending over in front of him to “pick something up,” ass cheeks spilling out of her shorts, thong string disappearing between them. Walking around in the evenings in tiny sleep shorts and a sports bra that looked painted on, “accidentally” moaning softly when she stretched. She’d catch his eye and bite her lip, giving him that look that said I know you want to fuck me.

But she never crossed the line with Scott. Not once. She called him “Daddy” in that sweet voice sometimes, but it was innocent — the same way a girl would with her mom’s boyfriend. She didn’t flirt with him. Didn’t give him fuck-me eyes. Didn’t grind on him or tease him. Scott was Lydia’s man. Stiles might be a filthy slut who loved cock, but she wasn’t going to destroy her mom’s happiness. Ever.

Derek noticed. And it only made him more obsessed.

A week after they moved in, Scott suggested a family movie night after dinner.

“Something fun,” he said, arm around Lydia on the couch. “We’re all living together now — let’s make it feel like home.”

Lydia beamed. “That sounds perfect! Stiles, come sit with us.”

The big sectional couch in the living room was huge. Scott and Lydia took one side, cuddled up under a blanket, already kissing softly between bites of popcorn. Derek sat on the other end, legs spread, trying to look relaxed in a black tank top and grey sweatpants that did nothing to hide the outline of his thick cock.

Stiles came in last.

She was wearing a tiny pink tank top that clung to her massive tits and a pair of the shortest sleep shorts imaginable — basically underwear. Her fat ass jiggled with every step. She smiled sweetly at everyone.

“Can I sit here, Daddy?” she asked Scott in that soft, innocent voice, pointing to his lap.

Scott chuckled, warm and fatherly. “Of course, sweetheart. Plenty of room.”

Lydia just smiled, happy her daughter was bonding.

Stiles climbed onto Scott’s lap like it was the most natural thing in the world — facing the TV, back against his chest, legs tucked to one side. She wiggled to get comfortable, her huge ass grinding down subtly against his thighs. Scott didn’t think anything of it; he just wrapped an arm around her waist like a dad would and kept watching the movie.

But Derek saw everything.

From across the couch he watched her. The way that tiny tank top rode up, showing smooth skin. The way her massive tits bounced every time she shifted. The way she kept wiggling — not obvious, but enough that her ass was rubbing in slow little circles on Scott’s lap. She looked so sweet on the outside, eyes big and focused on the screen, but Derek knew better.

Then she turned her head just enough to look straight at him.

Behind their parents’ backs, she mouthed the words slowly, clearly:

“I’m so wet.”

Derek’s cock went rock hard instantly.

He could see it in her eyes — the filthy truth behind the innocent act. She was getting off on this. Sitting on her mom’s boyfriend’s lap, wiggling that fat ass, getting her pussy soaked while mouthing dirty shit to him. His sweatpants tented obscenely. He shifted, trying to hide it, but Stiles noticed. Her lips curved into the tiniest smirk before she went back to acting sweet.

She kept wiggling.

Slow, subtle rolls of her hips. Grinding her clit against Scott’s thigh through those thin shorts. Derek could almost smell how wet she was from across the couch. Every few minutes she’d glance at him again, mouthing more things when no one was looking:

“Bet you’re hard.”

“Want to fuck this slutty pussy?”

“I’m dripping.”

Derek’s jaw was clenched so tight it hurt. His cock was throbbing, leaking pre-cum into his sweats. He wanted to drag her off that lap, bend her over the couch, and fuck her until she screamed. But he stayed frozen, glaring, cock aching while she played her little game.

Lydia and Scott were oblivious, laughing at the movie, cuddling. Scott even kissed the top of Stiles’s head once, completely innocent.

Stiles just kept grinding.

By the time the movie ended, Derek was in actual pain from how hard he was.

“Alright, time for bed,” Scott said warmly, helping Lydia up. “Big day tomorrow.”

Stiles slid off his lap with a sweet smile. “Goodnight, Daddy. Goodnight, Mom.” She gave Derek one last look — pure slut — before heading upstairs.

Everyone went to their rooms.

Derek lay in bed for hours, cock still half-hard, replaying the way she mouthed those words, the way her ass looked grinding on that lap, the way her nipples poked through that tiny tank top. He hated how much he wanted her. Hated that she was right next door.

Around midnight he heard it.

A soft sound from the hallway. A door clicking shut.

He got up, pulled on sweatpants, and stepped out quietly.

There she was.

Stiles was sneaking back into her room from the hallway, trying to be quiet. She was still in that tiny pink tank top and shorts, but now her thighs were shiny. Fresh cum was literally dripping down the inside of her legs, glistening in the low light. Her hair was messy, lips swollen, and she had that freshly-fucked glow.

She froze when she saw him standing there in the dark hallway.

Then she smirked.

Derek’s eyes dragged down her body — those shiny, cum-covered thighs, the way her shorts were damp at the crotch, the bite marks on her neck she hadn’t even tried to hide.

“God,” he muttered, voice low and rough. “When the fuck did you even have time to get railed and come back? What a fucking whore.”

Stiles’s smirk widened. She leaned against her doorframe, not even trying to hide the mess on her thighs. “Mmm… maybe I got a quick call from one of my regulars while you were all sleeping like good little boys.” Her voice was low, filthy, nothing like the sweet tone she used around their parents. “He came so deep in my pussy, Derek. Feel how much is still leaking out?”

She ran two fingers up her inner thigh, collected some of the cum, and slowly sucked it off her finger while staring right at him.

Derek’s cock twitched hard in his sweats.

“You’re disgusting,” he growled, stepping closer. His voice was full of disgust… and pure lust. “Parading around here like a sweet little angel for your mom, calling my dad ‘Daddy’ while you’re out getting your slutty cunt filled by random guys. You’re nothing but a filthy fucking whore.”

Stiles’s eyes sparkled with excitement. She loved this. “Aww, is stepbrother mad?” she whispered, stepping closer too. Her massive tits were almost touching his chest. “You were so hard during the movie… I saw that big cock tenting your sweats. Bet you wanted to pull me off his lap and fuck me right there while Mom watched.”

“Shut the fuck up,” Derek hissed, but he didn’t move away. His eyes dropped to her shiny thighs again. “You’re gonna get caught one day. Sneaking out to get fucked like a cheap slut while your mom is sleeping upstairs with my dad. You really are a whore.”

Stiles giggled softly — that sweet sound she used around everyone else, but her eyes were pure sin. “Maybe… but I’m a careful whore. And I only fuck guys who aren’t my mom’s man.” She reached out and lightly dragged one cum-slick finger down the center of his chest, leaving a shiny trail. “Unlike you… who clearly wants to bend his new stepsister over and wreck her.”

Derek grabbed her wrist hard, glaring down at her. For a second he looked like he might actually snap and fuck her right there in the hallway. His cock was fully hard again, pressing against her stomach.

But he didn’t.

He let go, took one step back, and glared at her like he wanted to murder her and fuck her at the same time.

“Get in your room, slut,” he said coldly. “Before I do something we’ll both regret.”

Stiles just smiled, licked her lips, and slipped into her room, closing the door softly behind her.

Derek stood there for a long moment, breathing hard, cock throbbing painfully. Then he went back to his room, locked the door, shoved his sweats down, and wrapped his hand around his thick cock.

He jerked off hard and fast, remembering the way she mouthed “I’m so wet,” the way her fat ass wiggled on Scott’s lap, the shiny cum dripping down her thighs, the filthy way she sucked it off her finger. He imagined bending her over, spanking that juicy ass red, and pounding into her cum-filled pussy while she moaned his name instead of “Daddy.”

“Fucking whore…” he groaned under his breath as he came hard, ropes of thick cum shooting across his abs and chest.

He lay there after, chest heaving, already knowing this was only going to get worse.

Living next door to her was going to destroy him.