Hot Summer Job/Agree to Kylie's suggestion
Kylie's suggestion is a welcome one. Having her innocent little sister work your meat is so very wrong yet insanely alluring. But this far in you need to at least try to keep up your act of stubbornness.
"She can do whatever she wants," you declare with an apathetic shrug. "You'll have to work really hard to make me cave."
Kylie's eyes nearly sparkle after your announcement. That's the closest you've come to saying 'yes' so far and Kylie couldn't be more pleased. For her it's now just a matter of getting Larissa to break you.
"Rissy! I have an idea!"
Kylie steps away from you, hopping down into a squat next to her sister. Larissa is still pawing cluelessly at her bare mound as her big sis whispers into her ear.
"Huh?"
Kylie whispers again, being sure to cover her mouth lest you discover their plan ahead of time. Larissa scrunches up her face, confused by the secretive words she's receiving.
"What's a blowjob?" she asks.
"Larissa!" whines Kylie, as if she's just ruined a cunning plan. "You don't know what a blowjob is?"
Rissa glances between you and her sister, brow furrowing slightly. She timidly shakes her head. "...no."
"Ughh," groans Kylie. "A blowjob is, like, when you suck on a boy's penis, alright?"
"Really? Why is it called that? Why isn't it a suckjob?"
"I dunno, it just is! Okay? Now come on." Kylie pulls her sister up off the floor. "Just do a blowjob already!"
The three of you stand together in utter silence in the girls' living room. All of you being naked and openly turned on does nothing to free the awkward teenage lust stuck behind your inhibitions while you stare each other down.
"You first," Larissa quietly prods.
"No!" Kylie sounds a bit defensive at first. "He said you can do anything you want. Not me," she adds, justifying her inaction. It seems especially weird after she just spent a couple minutes inquisitively pumping you to full mast. But maybe she's had her fill of cock for the day.
"Well..." The younger sibling shifts from foot to foot, picking at her bellybutton and her pussy mound at the same time. "Can't you just show me?"
"No, because I don't kn-... er, need to show you. It's easy. You just put it in your mouth."
More standing ensues, Larissa playing with herself indecisively. Finally Kylie takes action, pushing her little sis within range of you.
"There. Now suck it."
If she were to just open her mouth and walk forward Rissa could draw you in without any effort. She's at nearly the perfect height to blow you while standing. But Larissa grabs you midshaft and jerks you about instead, getting a better look at you while handling your erection like a joystick. It takes a minute for her to work up her courage it seems. Finally she leans forward, slides her lips over your head and takes your wet tip into her mouth.
Larissa sucks on you hard, as if your cock were a stubborn lollipop. She instantly sucks out all the precum stuck in your shaft, making your balls clench. You can see her make a weird face and glance up at you with further uncertainty. But she obediently sucks just as instructed, with one hand holding you steady.
"How is it?" Asks Kylie, clearly intrigued.
Larissa pops you out of her mouth, directing your shaft upward with her hand while she turns to address her sister.
"It tastes kinda funny."
"Like what?"
Rissa bends your cock down and looks you over again with interest.
"I dunno," she admits before sliding you into her mouth again, if only to figure that out.
Besides her constant suction, she isn't doing very much down there. After a few more moments of stationary sucking she pulls away again.
"Am I doing this right?"
Frankly she should be addressing that to you, but she again turns to her big sister for guidance. Kylie flippantly encourages her.
"Yeah, y'know, like... lick him and stuff."
The latest suggestion is well received. Larissa pulls back your foreskin (perhaps unintentionally) and starts licking your glans like a popsicle. Her tiny delicate tongue does tantalizing things to your dick. In no time another drop of precum finds it's way out.
"Put it in your mouth again," requests Kylie. She has one hand up to her own mouth with the other down at her crotch, her fingers circling and tugging on two distinct pairs of lips in tandem.
"Okay. Like this?"
Jaw dropping, Rissa inserts you into her warm little mouth once more. She continues to lap at the tip of your cock, tonguing your sensitive frenulum and drawing the latest of your lubricant from the stiff rod that she holds so firmly.
This is pretty amazing but it's mostly still a tease. You need more.