You voted for "A. Go and offer him a hand" (on tumblr, and AO3) with a total of 9 votes!

Enjoy ;)

The sounds of Natsu's heavy breathing and pounding heart nearly drowned out the little whimpers his brother made. He was leaning against the wooden door—the last obstacle that separated him from his older brother.

'I'm really going to do this, aren't I? Things could get awkward between us, but I just don't care right now. I'll forever wonder what the outcome might have been if I don't do this.'

He looked down at himself, clearly seeing the outline of a boner through his pants and let out a barely audible sigh.

He'd decided to play it cool. It would be best, both for his heart and for their relationship. Plus, if Zeref refused, he could just shrug it off and the awkwardness would be kept to a minimum.

He took a deep breath and braced for the worst outcome.

Zeref's clothes were already drenched in sweat, but he wasn't even close to finishing. Why was this so hard? With all the mental images of him doing lewd stuff with his little brother, it should have been easy to get off even with minimal friction. If only he didn't have to worry about keeping his voice down.

He bit back a frustrated groan. Shifting the angle and moving his hips quicker hadn't helped much. He was at a point where he'd do anything—maybe if he bent his spine so that he could sandwich his cock with his elbows...

A loud rustle from within the room nearly gave him a heart attack. He didn't dare breathe, could only stare at his pillow in horror. Surely he'd misheard. There was no way something or somebody was—

"Do you need help with that?"

Zeref whirled around, wrapping the blanket tightly around his body with the clumsy movement. He could only see silhouettes in the near complete darkness, but there was no doubt that Natsu was standing in his room, the door closed. When had that happened? How long had he been standing there? How had he entered without Zeref noticing?

But more importantly: "Have you ever heard of privacy or knocking?"

Natsu shifted from one foot to the other. "I thought you'd stop if I knock—"

"Well, that's kinda the point of it, yeah."

"—but I came here to offer a hand."

His mind replayed the words several times before he registered the meaning behind them. Judging from Natsu's tone, he was dead serious with his offer.

He could get Natsu's hand around his cock, stroking him, making him come. All he had to do was accept. He gulped.

"You... mean it?"

"Of course. It's partly my fault that Wendy didn't heal you, and I did promise I'd take care of you, right?"

Well, if he put it that way... Zeref was in need and Natsu offered his help. No strings attached. Natsu would be lending him a hand because his didn't function properly. Nothing else. There was no reason to refuse.

"If you don't want me to, I'll just go—"

"No."

"Oh? Very well, then I'll stay." Natsu crawled onto the bed, caging Zeref with his limbs. He leaned down and whispered right into Zeref's ear, "Relax. If it helps, imagine it's your own hand, or that I'm somebody else."

Did that mean Natsu hadn't noticed what was going on? That he didn't know his big brother was lusting after him? Well, all the better.

"Okay."

Extricating Zeref from the blankets proved to be a bit tricky with Natsu on top, so he stood up. Much to Zeref's disappointment, Natsu didn't lie back down once the sheets were on the floor, but instead sat down cross-legged next to Zeref's hips, facing his crotch. His knees rested against Zeref's thigh and abdomen.

Zeref closed his eyes, nervously anticipating the moment Natsu would take his clothes off. There was absolute silence, and nothing happened for a while. He wondered if Natsu had changed his mind and was about to ask, but then he felt something brush over his clothed crotch.

He threw his head back as a wave of pleasure surged through his body. Natsu's hand carefully massaged the tip for a while and then quickly removed all the clothes that were in the way. He wrapped his hand loosely around Zeref's hard cock and caressed the tip, smearing pre-cum all over it.

"Wow, you're wet. You must've been at it for quite a while already."

"Sh-shut up, ah!"

He bit his lip in an attempt to stifle the embarrassing sounds that left his mouth, but he didn't manage to suppress them completely.

"I will, but only if you don't hold back your voice. Remember that you promised Lucy you wouldn't suppress your feelings anymore? This is a feeling, too."

What a joke. If he didn't suppress at least some of his current feelings, he'd scare Natsu and probably everyone else he knew away. Besides, what had holding back sounds of pleasure got to do with anything? Zeref opened his mouth to protest, but Natsu chose that exact moment to start pumping him eagerly, so all that came out were moans.

"Mhh, good, let it all out. There's nobody who could overhear, and it feels best if you're not holding back, trust me."

What a dirty tongue his brother had! As if his hand wasn't already driving him crazy enough. Oh, how Zeref wished he could see Natsu's face clearer, but it was blurry in the shallow moonlight. Natsu was staring at Zeref's face, that much he could tell, but even Natsu shouldn't be capable of seeing his expression, right? Or was he able to see in the near darkness thanks to his enhanced senses? Could he see Zeref's lustful face, his parted lips, his eyes searching for something they wouldn't find? He wanted to know.

"C-can you s—ah, ahh, Natsu, stop!"

The hand slowed down to the point where it was merely a lazy caress.

"Gonna cum, nii-san?" Natsu asked, his voice raspy.

The words echoed in his mind. Images of Natsu and himself popped up. Natsu with his cock buried inside Zeref's ass, pounding into him like there was no tomorrow, pumping Zeref's cock until he was screaming Natsu's name. Gonna cum, nii-san? Me too, I'm gonna blow my load so deep into you—

"Shit, I'm about to—nghh, ahhh!"

Waves of pleasure rocked his body as he came hard, spilling his release all over Natsu's hand and his own clothes. Natsu worked him through it, slowly coming to a halt when the twitching of his body subsided.

"That was rather quick. You had a lot bottled up, hm? That's not good for your health, nii-san. You should take care of this once in a while."

Zeref heard the words, but he didn't understand the meaning of half of them. He was too out of it, reveling in the powerful orgasm he'd just had.

He distantly noted that Natsu withdrew his hand and clumsily wiped the mess inside Zeref's clothes dry one-handed. Then he got up from the bed, holding his soiled hand up lest it spoiled his clothes or the floor.

He was already nearly out of the room when Zeref finally had enough presence of mind to realize that he shouldn't let Natsu go like this.

"Wait."

Natsu paused, looking over his shoulder.

"Yes?"

Zeref sat up, hoping that the upright position would give him back at least a little bit of his dignity.

"This... what was... um."

Very dignified indeed, stuttering like that.

"Just me lending you a hand because yours are useless right now. We don't ever have to talk about it or even acknowledge it happened."

Something inside Zeref broke, but he nodded anyway.

"Thanks."

Natsu turned his head back to the corridor and gave a nod as well.

"Good night."

After the sound of the closing door died away, the heavy silence that followed threatened to choke him. There was the faint sound of Natsu locking himself into the bathroom, but then there was nothing to distract him from the panic that welled up inside his gut.

'I let Natsu touch me. I tainted my little brother. All for a few minutes of selfish pleasure. And what now? How will I face him in the morning? How will we face his—no, our friends? Why haven't I chased him away?'

Zeref noticed that he was crying only when a tear entered his parted lips, spreading a salty taste in his mouth. He wiped his cheeks with his bandaged hands, but it was no use. New tears just kept wetting them again.

Natsu was about to hold his cum-covered hand under the jet of water when curiosity got the better of him. He brought it to his lips, licking up a bit of Zeref's cum. It didn't taste good, but the fact that he was tasting his brother's cum turned him on. Not that he needed the additional stimulation after what he'd just done. When his brother's hot seed had coated his hand, he'd feared for a moment that he would come untouched. He hadn't, so he was still achingly hard.

Maybe he could make good use of the sticky liquid. He closed the tap.

Once his pajama pants and boxers were out of the way, he wrapped the spoiled hand around his cock and slicked it up. He never once took his eyes off his dick as he brought himself closer to the edge, alternating between moving his hand and moving his hips while imagining the hand was... something else. Namely, his brother's mouth or asshole.

In his head, it wasn't his foreskin sliding back and forth over his tip, but Zeref's wet lips. His brother would fondle his balls. He'd lick over the tip every time his head bobbed up. Maybe hollow his cheeks to increase the friction. Natsu would tell him how much he liked being sucked and then his voice would break, and he'd come hard—

"Ah, holy shit!"

Natsu angled his cock so that the spurts of cum landed in the sink, then closed his eyes and enjoyed the ecstatic waves of his powerful orgasm.

When the aftershocks faded, he looked up at his reflection, breath coming quick and ragged. He would have thought he'd feel guilty for his actions, but he didn't. Zeref had felt good, Natsu had felt good. Something that was supposed to be wrong shouldn't feel that right. He wasn't going to apologize, neither to Zeref nor to himself. If he was ever presented with the opportunity to do it again, he wouldn't hesitate.

Persistent knocks threatened to pull Zeref from the sweet embrace of his little brother, but he didn't want to leave just yet. It felt so good, and he knew that Natsu felt the same—he'd told him so.

Another knock, harder this time. "Hey, wake up! Can I come in?"

Zeref startled awake, sitting up straight. The events from the previous night crashed over him like a waterfall, and his brief hope that it had all just been a dream were shattered as he lifted the blanket and saw that the only thing covering his crotch was his sash.

"Heeeey, big brother, are you awake?"

Zeref wanted to bury his face in his hands, but when he hit himself rather hard with the bandage balls, he cursed.

"Yeah, I'm awake."

"I'm coming in then."

The door creaked, revealing a cheerful Natsu.

"Good morning, sunshine."

Zeref grumbled. "I said stop calling me that."

Natsu came closer and squished Zeref's cheeks. "Aww, but you're always in such a good mood in the morning."

"Mmmpf. Let go."

Natsu's behavior took a load off Zeref's mind, but he didn't let on. His little brother was damn good at not acknowledging that something happened between them.

"Okay, but you're accompanying me to the bathroom now, and you're getting a bath. The preparations for Fantasia Festival are starting today and I don't wanna be late."

Seriously, how could Natsu still think that taking a bath together was a good idea after what happened the previous night?

"I told you yesterday, I don't want to take a bath."

"Nu-uh, you told me you would figure something out and that you were too tired and then you just kicked me out of your room. Have you figured something out? I'm not taking you to the guild reeking like that."

Natsu made a mock-disgusted face while pointing to Zeref's armpits, which earned him a bandaged smack on the forehead. Natsu laughed and launched a counter-attack, and after a short scramble, Natsu had Zeref pinned to the bed, sitting astride his hips.

That left Zeref's crotch directly under Natsu's, separated only by a few layers of thin cloth. Panic kicked in. Zeref knew all too well that Natsu was physically stronger than him, but that didn't stop him from trying anyway, frantically rocking his hips in an unsuccessful attempt to throw Natsu off. Very bad idea. As if he'd needed additional stimulation to get stiff.

"Get off!"

But Natsu only leaned down and whispered right into his ear, "You have two options. Either I'll bathe you or I'll ask Gray to do it. You decide."

If Natsu had already noticed Zeref's semi-hard-on, he didn't let it show. However, Zeref needed to answer quickly, before it was too late.

A. Pick Gray
B. Pick Natsu
C. Refuse to answer, panic instead (because panicking is always a good idea), try to get Natsu off desperately (pun totally not intended, I swear)

I realized that offering an open answer which you should clarify is a bad idea since it's never gonna make it. Most people don't read the comments of others before they write their own.

Update 17.03.2019 (March 17th, 2019 for those among you who aren't used to the European way of formatting a date): Currently, we have a draw between the options A and B, counting the votes on AO3 (3x A and 4x B) and the votes here on (2x A and 1x B).
The next vote I get will be the last and determining one, no matter on which platform.
Even if the next vote is for C. In this case, I'll decide on either A or B (insert evil laughter here).

Another update (same day as above): Okay, it's decided, it's going to be B! ABeautyFairy (on AO3) left the final vote, the poll's closed!