Ace loves his brother dearly, knows he'd always be there for him should he need it, and that he is the best person in this whole wide world.
However, he is a fucking brat in the bedroom.
Luffy and him are both pretty chill men (at least, if he'd have to say so himself,) and so when he'd approached him on the subject of starting a beneficial relationship with each other as to relieve stress or just get that good ol' dopamine racing (well in his case), he wasn't surprised when Luffy didn't see a fault with it.
It's been nearly a year, and during that experimental time of his life, he's figured out a couple things about himself.
1) He's pretty versatile and fine being top or bottom.
2) New boundaries and preferences.
and
3) He likes it when it hurts.
The first time he made this discovery was during an intense orgasm on Luffy's part had his brother make red lines down his back, which had caused Him to climax right after.
Needless to say, he'd been pretty embarrassed at first (it was a pretty new thing at the time,) but Luffy'd just smiled coyly and ever since then he'd dig his nails a little deeper or nip with his teeth here or there like the goddamn tease he is.
But not tonight.
Tonight, Ace had a plan to give it back.
The seed had already been planted, he'd found Luffy on the couch scrolling on his phone and he'd asked if he'd wanted to have sex tonight (or, as his brother says it, do 'the sex') and the man in question had nodded and said sure.
It was now night, they'd eaten dinner a few hours earlier and Ace were now waiting in his bedroom, putting his lube on the counter by the bed.
Luffy, ever his graceful self, walks into his room butt-naked, not knocking or anything, and just lays down on the bed spread eagle.
"You wanna top?" He asks Ace, who's in the middle of undressing himself (he'd feel weird standing in his room naked,,)
"Yeah. That cool with you?"
"Mhm. You got any specifics in mind for tonight?" His brother crosses his arms behind his head and looks up at him with curious eyes.
Keeping his face as natural as possible, he answers.
"I do. You just lay back and enjoy it alright? Stop me at any time if you want."
Pulling his boxers off as the last article of clothing and throwing them across the room, he places his knees on the mattress, feeling it dip beneath his weight.
Reaching out, he lifts Luffy's face by his chin as he towers over him, slowly lowing himself to be between his spread legs. His brother automatically closes his eyes and opens his mouth slightly, Ace licks his lips before leaning in, letting his tongue trail the inner side of Luffy's lower lip.
As their tongues dance, his hand trails slowly from his chin, down his neck where he can feel the speeding up pulsing of his heartbeat, and lower till he stops by his brother's tan abdomen.
Breaking the kiss, his tongue trails the same road, making small nips here and there.
His mouth keeps going till he's nosing the dark nest of black curls, his hands coming up to spread Luffy's thighs a little bit wider, kissing the inner sides of each leg before slowly trailing his tongue on the hot skin up his brother's shaft, feeling it harden and twitch from his exhales.
Luffy's not the most sexual person (in which Ace'd once asked him why he agreed, and Luffy just replied he liked trying new things, it felt good and he could spend time with Ace. Ace respected that,) but as their time together progressed, so did his brother's sexual nature.
He rarely comes to him and asks for sex, doesn't care much and doesn't think about it (his words, not Ace's) but he'd said he enjoyed it.
Letting his tongue continue further up and away from his brother's dick, he creates a slow pattern.
Down, thighs, up the shaft, stop at navel. Repeart.
He keeps this going, till he hears Luffy's breathing deepening and till he sees those hard hooded eyes gleam with slight impatience.
During this round, he strays a little longer at the inner side of his thigh, letting his tongue dance by the muscles and mapping out freckles similar to his own on the tan skin glistening with sweat and spit.
His teeth trail over the skin, feeling it move in response, he bites lightly before sucking and making a mark.
Luffy's breath hitches in response, and Ace fights back the urge to smirk.
He gives his brother's other thigh the same treatment, before slowly making his way to the neglected erection.
It's head is angry red and slightly shiny with precum, Ace reaches out with his hand and let's his fingers trail with nails first up and down the shaft, before he closes his fingers around it in a tight but not bruising grip, and leans down to take it into his mouth.
Luffy groans and raises his hips a little in a bucking motion, so Ace keeps him in place with his free hand as his head bops up-and-down.
He lets his brother fist a hand in his hair, it helps keeping it out of his face.
Luffy's other hand is gripping the bed sheets, his breathing louder by the minute as Ace picks up the pace.
Feeling the tell-tale signs of his brother's coming on climax, he pulls off his dick, licking his lips and wipes the saliva and precum mix off his chin.
His brother watches him with glazed over eyes, the shaking in his legs dying down now that he's not on being stimulated, mouth hanging open slack jawed and face flushed red.
It's a delicious sight.
He reaches out for the lube, flicking it open with a practiced move.
Grimacing a bit, because he always forgets that it's scented, and wonders, again, why they still haven't replaced it as they keep on using the mint scented lube.
After a particularly rough night full of sex he'd once gone to work where Marco, his coworker, asked if he'd bought a new extra strong smelling toothpaste.
Ace has never gotten so red in his entire life trying to play on a lie like that.
Ignoring the scent to the best of his abilities, he focuses instead on preparing his brother for him.
Slowly starting off with one finger down to the knuckle, before adding another one and scissoring them, kissing Luffy on his chest and making a few more marks while doing so.
Adding a third finger, his hand pumps his brother a couple times to help him getting used to it, and when the groans start up again, retrieves his hand before putting the excess lube from his fingers on his own dick.
He bends Luffy's knees and reaches for the pillow to put under his brother's hips. Luffy thanks him and spreads his legs as wide as he can in that position.
Lining himself up, he slowly pushes the head in inch by inch till he's buried deep in that white hot heat, keeping eye contact with Luffy as their equally dark eyes communicate in the dark.
He waits a moment to let his brother adjust to the intrusion, his finger tracing the barely there freckles on his face, and the scar beneath his left eye.
It will always amaze him that no matter what, Luffy has always looked at him with absolute trust in his eyes, like he'd hung the moon itself.
And Ace will never do anything to betray that trust for as long as he lives.
"Alright, you can move"
He starts with a slow but steady pace pulling out about halfway before pushing back in.
When the hitches and moans slowly start back up again, he speeds up before getting up on his knees with a tight grip on Luffy's hips.
He lifts one of his legs and puts it on his shoulder, before pulling nearly all the way out and slamming back in.
Luffy oofs before throwing his arms up and arching his back for a better angle. Ace adjusts his hips slightly, knowing where to hit to make his brother scream in pleasure, but knowingly barely graces it.
Huffing, he tries to speak, making Ace's hairs stand on edge.
"H-harder. You can do b-better than this, can't you?"
Luffy smirks that stupid bratty smirk of his, meeting his eyes in challenge.
"G-Give it to me"
And Ace doesn't need to be told twice.
Bending his torso and being hold up by his palms on the bed, he leans over Luffy and sets and absolutely brutal pace.
His brother's leg is still bend over his shoulder, his head is thrown back and eyes are barely open as he breathes heavily and fast, hair stuck to his sweaty forehead and face completely flushed.
He doesn't know what it is, but something in him tells him to bend down and latch on - he growls, a throaty deep sound from within and leans down before biting his brother hard on the junction between his shoulder and neck.
Luffy nearly howls and he feels hands and harsh blunt nails trail scorching roads of fire down his back, he growls again and bites again, further up the sides of his neck.
He makes sure to lick them apologetically afterwards of course.
Angling his hips just right, he repeatedly slams down on his brother's prostate as he plasters more and more bites in the neck area.
His brother's thighs shake and muscles tense up before completely spasming - feeling something wet, Luffy's crying, both literally and out in pleasure as he climaxes.
That and coupled with his brother's nails down his back makes him only a few thrusts behind him till he's coming himself.
He rides out both their orgasms, slowly slowing down before rolling off Luffy to lay besides him so they can catch their breath.
They lay there for what feels like ten minutes, before Luffy sits up and smiles down at him.
"That was neat!" He says like the absolute dork he is. Ace doesn't bother fighting back a snort.
"Yeah, it was."
That night, after they both showered, they fell asleep on the couch watching a movie.
He felt like he'd given back well enough.