Chapter Text
It was a torn feeling in Izuku’s chest when his parents divorced. It wasn’t out of a lack of love necessarily; his father being the number one hero in Japan came with a lot of dangers. Although, he did wonder if that was just what they told him when he was too young to understand falling out of love.
But Izuku never resented his father, even when he moved abroad to the United States after his official retirement from hero work. In fact, it just made the opportunity to see him more exhilarating when he was finally able to block out his summer break to visit. He knew from their calls that his dad had remarried to an old college fling he had before he met his mom. Apparently the man, Dave, had a daughter around his age too.
Izuku had been so excited that he’d barely slept in the days leading up to his flight and despite that he still had the energy to spring into his father’s arms once he landed.
“Zuku, my boy!” Yagi coughed harshly as the teen barreled into him, still smiling nonetheless. “Ah…I missed you…”
“Dad, it’s so good to see you!” Izuku exclaimed, voice muffled a bit as it stayed buried in his dad’s oversized coat.
Toshinori took a moment to ruffle his already messy hair before grabbing one of the luggage bags Izuku had abandoned a few feet away to free his arms. “Dave has the car outside, let’s not keep him waiting.” Izuku only nodded and scampered to grab the rest of his things, trailing behind him like an eager duckling.
As they got outside, Izuku spotted a tall girl with bright blonde hair waving to them. That must be Dave’s daughter. “Hey! You must be Izuku,” she grinned and trotted up to greet him.
“Y-Yeah, uhm, Melissa, right?” Izuku guessed. He remembered hearing her name before but not enough to be confident in his answer.
“Aw, you remembered. It’s so great to finally meet you in person, little bro.” Izuku found himself blushing a little at her already giving him a familial nickname.
Dave chuckled a bit as he leaned out the passenger side window from his spot in the driver’s seat. “She’s been looking forward to this trip almost as much as you have.”
“I never had any siblings growing up so this is kinda surreal. But in a good way,” Melissa admitted.
“Yeah, I guess that’s the best way to put it…” Izuku smiled and followed Melissa to the car. He hadn’t really thought about it but having an older sister for a while sounded great!
By the time they’d driven back to the house, Izuku was finally suffering the consequences of barely sleeping, getting up for a long flight, and burning all his energy talking with everyone. He'd completely passed out during the ride back to his dad's home. He hadn't even realized he fell asleep at all. He opened his eyes with a groggy groan when he heard the car shut off but was quick to close them again.
Still not having the energy to wake up, he laid his head back on the warm pillow supporting him. He heard Melissa stifle a giggle before he felt a slim hand running through his hair. He opened his eyes again, his mind remembering that there hadn’t even been any pillows in the car. What was he laying on??
“You comfy down there?”
Izuku’s eyes trailed from her grinning face down to where his cheek was pressed against her chest. The thought hadn’t crossed his mind earlier but now he was practically forced to acknowledge his step sister’s massive boobs, much to his own embarrassment. “Ah- s-sorry, I didn’t- um…” Izuku sat upright and flushed even as Melissa smiled and laughed off the awkward position. “I ah, I should go settle in…”
“I’ll show you the guest room, Izuku,” Toshinori chimed in with a smile, having not noticed the position the two kids had been in at all. Izuku took the excuse to leave the awkward situation as he slipped out of the car and grabbed his bags with his dad’s help.
Izuku didn’t have much time to take in the large house, eyes fixed on his feet as he toed off his shoes at the door and followed Yagi up the carpeted steps to the second floor. With any luck he could just take some time to decompress from his flight and forget that twinge of embarrassment ever happened. The boy was so lost in his head that he ended up bumping into his dad once the man stopped to open the door.
“Whoa- heh, guess you’re still tired from your flight, huh?” he chuckled as he let the bedroom door fall open.
Izuku smiled sheepishly and nodded, “Y-Yeah, sorry…” He looked past his dad and into the spacious guest room. There was a faint scent of cleaning supplies and vacuum dust still in the room but they’d clearly worked hard to make sure it was spotless. The bed was neatly made and looked irresistibly soft. It looked like he had his own bathroom as well, the door ajar on the left wall of the room.
“We’ll call you down for dinner. You go ahead and get comfortable Izuku.” With a light pat to Izuku's back, Toshinori turned to leave the room.
Izuku smiled as the door shut, a small rush of energy returning to his body as he dropped his bags by the bed and trotted over to investigate the bathroom. A long night up, a long plane ride, and a long drive. None of these were particularly taxing but he'd gone longer without washing up than he would've liked. Plus, it was his first dinner with his dad and his new family. Of course he should be more presentable.
Izuku peered into the large oval tub, it'd be more than comfortable for his small frame. Hell, this thing could fit two people if you tried. He figured out how the drain plug worked and turned the dials by the faucet, fussing with them every few seconds to get that perfect steamy temperature. He peeled off his clothes that stank with the indescribable smell of a long day of travel, dropping everything into a small pile on the counter.
The water reached deep into Izuku’s bones the moment he sank into the tub, forcing a relieved sigh out of his throat and he leaned his head back. In his haze of relaxation, he could’ve sworn he was forgetting something. As much as he was trying to enjoy his bath, his brain was dwelling on it. Obviously he took off all his clothes, found a towel, and the door was…wait.
Midoriya froze, his body tensing as he heard the door to the bedroom open again. Okay, nothing to worry about, yeah he didn’t lock the door but the bathroom door was at least shut. No one would just-
And the bathroom door swung open before he could even formulate that thought.
Izuku yelped and turned to the door, his body curling against the edge of the tub to hide his shame.
“Hey there!” Melissa greeted, waving to him as if he was not currently naked with his clothes too far to reach.
“M-Melissa!! Um- I’m kinda busy here?” Izuku squeaked, trying to usher her to leave without using his hands that were currently stuffed between his legs to cover himself.
Melissa just smirked and strutted forward, hips bouncing outward with each step. She adjusted her glasses and sat down on the edge of the tub, eyes never leaving Izuku’s body. “I heard you starting a bath and I just realized; you don’t have a lifeguard here at your beach,” she said with a wink.
Izuku just stared at her, confused and uncomfortable, “I…I’m not at the beach, this is a bathtub???”
Melissa’s smirk didn’t waver as she leaned closer to him. "I'm just looking out for my new, cute little brother…" she purred as her slender fingers popped the top button on her shirt. Izuku swore he felt his brain fry as his face burned a bright red.
Melissa's eyes flicked down and a mischievous hum rose in her throat. "You like that? Calling you my little brother like this? Sounds extra naughty, doesn’t it," she stopped opening her shirt and dipped her hand into the water. Even in all his attempts to hide himself, she had still noticed Izuku's cock beginning to stand at attention. He gasped softly as her slender fingers ran over his cock, confidently wrapping around his shaft and pumping him slowly.
Melissa was right, this did feel naughty and forbidden, but if anything that made it better. She smirked and leaned closer to Izuku’s ear, teasingly nipping his lobe. “If you want more, I already stretched myself earlier. Just say the word baby brother…” she hummed.
Izuku moaned and arched into the hand stroking him. It felt good but it was far from enough. “Ahh- ‘lissa, big sis please…”
Melissa’s smirk grew wider as she stared down at her little step brother’s flushed face. She let go of Izuku’s dick and moved her hands back to her shirt, popping each button with quick precision as she let her shirt fall off her shoulders. She let her chest rest on the rim of the tub as she squirmed out of her pants, intentionally giving Izuku a tantalizing view of her boobs still framed by her plain, cream colored bra.
She kicked her pants and underwear off her leg and rose back to her feet, standing over her timid and horny little step brother as she stepped into the tub, legs on either side of his small frame. Izuku was practically drooling as he stared up at her helplessly, her fingers reaching down to spread open her cunt for him to see.
A whine rose in Izuku’s throat and Melissa chuckled. She leaned down and gripped the sides of the tub, lowering herself gradually. Her knees hit the bottom of the tub and she leaned into Izuku’s body, caging him in as she closed in on his mouth. Izuku mewled into the sloppy kiss, his tongue clumsily trying to keep up with his big sister. His hips arched as he gradually lost the air in his lungs, sloshing the water and desperately searching for friction again.
Melissa kindly answered his request as she ran her hand up his cock again. “So needy, you really want your big sis that bad, huh?” she teased lightly, breathing out her words into his neck. She smirked wider as his freckled skin bloomed with goosebumps.
"Please- I do, I really do!" Izuku begged, his hands reaching up to wrap around her back, trying to push her down onto his cock.
Melissa kissed him again with an amused hum, her glasses starting to fog up from the steam of the water. She sat back up, legs shifting a bit as she held her step brother’s dick steady. Both of them groaned as the head of Izuku's cock pressed against the entrance to Melissa's cunt.
Melissa gripped the edges of the tub again, her chest heaving as she pushed herself down inch by inch. The drag of his cock against her hot insides made Izuku moan shamelessly loud, his eyes squeezing shut. His hands gripped her waist and she finally settled, his dick fully sheathed inside her as they both caught their breaths.
"Told you it'd feel good…" Melissa sighed out as she raised her hips. Izuku groaned at the drag on his cock, head craning back and bumping the wall of the tub. If he had a bruise he didn't feel it over the sensations washing over his sensitive cock.
Melissa preened a little at the desperation so plainly written all over Izuku's face but kept the rock of her hips gentle and slow. She cupped Izuku’s cheek, her thumb lightly running over his bottom lip as his mouth stayed slack, letting every shameless noise fall out without even an attempt to mute himself.
The water around them swayed and bobbed with the roll of her hips, waves licking higher up Izuku's body as her pace grew faster. Melissa moaned and braced her hands on the wall behind Izuku, indulging in her own pleasure like her step brother was just another one of her toys.
"Such a good baby brother for me," she breathed out, slamming her hips back down on his cock and reveling in the loud, whiny moan that came from the boy below her.
“T-Turn over-! ‘lissa…” Izuku mewled as he grabbed Melissa’s shoulder and tried to push her over. Melissa sighed and went easily, holding Izuku close to try and keep his cock inside her. The wet walls of the tub helped them shift over as Melissa wrapped her legs around Izuku’s middle and laid her head back against the sloping wall of the tub.
Izuku whined and thrusted into her the moment his knees were firmly planted on the porcelain, gasping and panting as his quick, desperate thrusts sloshed the water surrounding him. Melissa’s name came out in a jumble of pleads and moans as he threw his face into her chest, just barely sitting above the water.
“Ahh! That’s right, fucking me so good baby brother…” Melissa sighed as she ran her hand through his wet, matted hair.
“S-Sis, sis! I ca-an’t stop!” Izuku mewled into her skin as his thrusts became even more desperate and erratic.
Melissa sighed out a moan as she arched her back, her other hand dipping beneath the water to rub at her clit. “My little brother close already? Fuck- come on. Come for your big sis!” she let out a heavy, desperate breath as she abused her clit, toes curling as her orgasm rushed her.
Izuku’s rapid thrusts, faltered, hands scrambling to hold onto her as he buried his cock deep inside her. He moaned and hiccupped as he came, his cock throbbing as he spilled into her. A dirty part of himself wished they hadn’t done this in the bath so he could see the aftermath but he didn’t let the thought taint his orgasm.
Izuku savored the feeling of his softening cock still being held in his sister’s warm cunt, her arms reaching up to rub his back and hold her spent little brother close as the bath water started to go cold. He could only hope he wouldn’t wait too long to fly out again. This visit was already off to an amazing start.