"Wait, what're you-?"
Seeing bloodlust in his sister's eyes, goosebumps shrouded every facet of Steven's body.
"Si-Sis! Wha-?!"
Selena's right-handed fist breezed past his face, and from the shockwave that followed, the mountain behind was blown to kingdom come.
Turning the panic-stricken Steven's head in the mountain's direction, she smiled as he paled.
"You... were this strong all along, Selena?
"I'm an operative of the Supreme Agency, Steven. Most heroes and villains can't come close to my level of power."
In quick succession, he inhaled and exhaled, still can't believe what he was witnessing.
"You know," she spoke,
whispering in his ear,
"I think you can take that punch."
"Are you insane?!" he shrieked in dreaded horror.
The laugh of his sister rang in his ear, and before he could speak another word she'd already created some distance between them; some feet away.
Clearing the distance, she reeled back her right arm; slowly this time, and she roared, giving her absolute best.
"Ahhh!"
While his scream echoed about, Selena's fist went to strike his face, but instead, it seamlessly slid through - akin to the effect of punching a ghost.
His clothes fell to the ground, and his sister's eyes widened. Selena puffed out--trembling--while retracting her fist.
"Steven..."
"Holy shit, Selena..."
"Why... do you have my unique ability... and every other ability I possess? And after cumming inside me, no less?!"
Steven paid no mind to his sister's words, gazing at her in terror as one would a monster.
Noticing his apprehension, Selena reached out toward him, quietly calling,
"Steven."
He backpedaled, gulping.
"You," he whispered,
"actually tried to fucking kill me, Selena."
Selena closed her eyes. Inhaling, she unfurled them to say,
"That punch of mine was going to be but a light tap. Why else do you think it was approaching so slow, Little Brother? I merely wished to uncover your unique ability."
He pursed his lips.
"Ah."
He burst out laughing.
Selena giggled.
"Holy shit, Sis! You almost literally scared the shit out of me!"
His sister began laughing alongside him. Shortly, they stopped. Steven was beaming. Selena's face was contorted into an expression of lust and intrigue, however. His naked body distracted her, and so--before he knew it--she dressed him.
"Steven, you have all my abilities; albeit to a far lesser degree."
Losing his smile, Steven nodded.
"Hm-hm."
"And you attained them, this new physique, right after finishing inside me."
"Hm-"
His sights grew expansive.
"Wait, are you saying my unique ability's-?"
She gave him confirmation, crossing her arms with a nod.
"Correct. Fucking me gives you my abilities, and mine alone, it seems. The maid, that Darlene: her unique ability allows her to hear the desires of others in her proximity, yet you clearly hadn't acquired that ability upon fucking her, for she had first told us it spontaneously activated out of the blue in the beginning. I alone give you strength."
Steven smirked, visage teeming with excitement.
"Awesome. So you agree that I was right, yeah? You really are... something truly special, Sis."
Selena blushed, involuntarily beaming and resting her arms at her sides.
"Look who's speaking of special, the man who gains his sister's abilities upon cumming inside her."
Something about her words stuck with Steven. He placed a hand under his chin, and thoughtfully gazed off into the distance.
"Selena, do you think it's only because you're my sister?"
"I'm not su-"
Realization crossed her features, and her mouth went agape.
"Steven, you're not thinking it's possible to, too, gain our sister's abilities by cumming inside them, are you?"
"I don't know. Maybe."
He threw a wry smile her way.
"Why that face? Feeling jealous, Selena?"
Profusely blushing, she scoffed.
"Please. I'm a grown woman, Steven."
Steven stepped forward, causing her to look unsure.
"You're right."
He put his forefinger before her face, letting it waver before her slightly parted lips.
"You're right, you are a grown woman. One who gets off at the thought of her precious little brother beating his dick to her."
Lust over her almost sedated countenance, she murmured,
"Yeah."
Before the elated Steven could run his mouth, Selena drawled with panic creasing her features,
"Anyway... Before you'd raised that question about our sisters, I devised the hypothesis that you harbor the ability to evolve each time you cum inside me."
Looking enticed by that idea, Steven voiced with a grin,
"Well, I'll be a sisterfucker."
Selena closed her eyes, unable to hold in the chuckle that rolled from her lips after.
"Okay. Very clever. But only after I'm done with work. I'll be sure to book motel rooms for both of us each night. Can't have the other girls finding out about our... special relationship."
Eyeing her deeply appealing cleavage, he said,
"Wholly agreed, Sis."