Chap 1

It was after his meeting with Hashirama that Madara felt it.

The young boy stopped walking. One of his hands came up to pull at the thick material of Uchiha clothing while the other wiped sweat from his pale face furiously.

"Hot" He thought, eyebrows furrowed. A few minutes ago Madara had been fine, even a bit cold from that stunt his friend pulled (you don't push people into the water while they are peeing; for god sake; you don't stand behind them while they are doing it at all!). Plus, the sun was sinking low on the horizon and cold wind was picking up. Yet, he felt as if he had just come out of a fist-fight with ten shinobis.

Madara wrapped a protective arm around his torso. Something warm seemed to be spreading in his stomach and his lower back ached.

Maybe father would know.

With that thought, he started moving again. However, the boy hadn't got too far before dropping to his knees; little body folded in half like an invisible man just kicked him hard in the gut.

Madara gasped, hot air rushed into his lungs. He then tried standing up but quickly fell back to the ground, limb shaking violently. There was more sweat and something disgustingly sticky was leaking onto his inner thighs.

He cursed loudly, the Uchiha compound was not too far away yet Madara found no energy to keep walking.

Damn weak body

And the heat was killing him.

Heat

Terror crossed his face. Of course, all the symptoms, how could he be so dense? Madara had even seen it before; he just never thought that it would happen to him of all people.

-Flashback-

Madara held his older brother's hand tightly. Which one? He couldn't recall as it was long ago. His onyx eyes glued on an isolated tent in which groans and screams were coming from.

Earlier that day, a kunoichi was carried back to their compound, face red and body curled up. No one dared to approach her. There were orders and temporary shelter was set up so the woman could rest. Then, three Betas guarded outside her tent. They shot anyone walking by dirty glares.

"Is it a contagious disease?" He asked.

"No, it's just a heat."

"Seem painful."

Madara stated, a childish fear suddenly occurred his mind:

"Will we catch it?"

"Nah, only Omegas have heat."

"But isn't she a kunoichi?"

All kunoichis and shinobis were either Alphas or Betas. There was a war after all and their clan couldn't risk getting the child-bearers into harm ways, sending children to battles was bad enough.

His brother shrugged:

"She probably hid her real gender somehow. Now that everyone knows, she would be getting into a lot of troubles. Omegas aren't meant to fight you know."

"What if I become one too?"

"Don't worry; you'd probably turn out to be an Alpha like us, or at least a Beta. Male Omegas are really rare."

Madara felt relieved. Good. He wanted to be strong like his brothers.

They walked away to the training ground; the woman's agonizing sound followed them.

1 week later, the kunoichi got married to an Alpha. Even as a child back then, Madara swore those two had nothing in common.

1 year passed and he ran into her again, this time with 3 pups. The woman wore yukata instead of armors like that fateful day her comrades brought her back. Her dark eyes were filled with sorrow and they haunted him for months. Since then, he prayed he would never become an Omega.

-Flashback ends-

It seemed that life hates his gut.

Madara breathed out in defeat. Somewhere behind him, a strange shinobi (Madara could not recognize which clan he was from) appeared. On his face was a Cheshire grin that screamed predator. The man also smelled foul, like burning flesh and something else Madara couldn't describe.

In the future, the Uchiha would recognize that other scent as "arousal", a sign warned him to get the F away from whoever it came from. But back then, Madara hadn't known it yet. So he just sat dumb folded.

The stranger chuckled. He gripped one of the boy's legs and dragged him closer on the dirt floor.

"Hn!"

Madara yelped, his sense finally kicked in and he thrashed. That did not deter the man, however, when nose sniffed his sensitive exposed neck and hands started groping him everywhere.

He head butted his offender, hard. The older man felt backward, giving him enough space to wiggle free and scrambled away.

"You little shit!"

Madara was tackled face-fisted into the ground. Next, angry growls were right above him and without looking, he knew that a set of eyes were glaring dangerously. Hot breath returned to his neck, making it all tickling.

The young shinobi whined. Maybe the other man would kill him, by biting his head off, perhaps, judging by the sound of teeth gritting and how hard he was pining him down.

This is it. I'm going to die.

Madara squeezed his eyes shut, waiting for his opponent to strike. The man above chuckled sadistically, obviously enjoying the sign of submission. His cruel hands tighten around smaller wrists to the point of leaving bruises.

Any minute now, Madara thought, counting down from 10 to 1 in his head. But the pain never came. A foreign growl, then the weight on top of him was pulled off.

Bewildered, Madara jerked his head around to look, just in time to see the shinobi's throat sliced by no one else but his very father.

Tajima looked down at his son, sharingans scanned for any possible injuries from that trash he just killed. He was furious. His hand gripped the bloody kunai tightly. No one touched his family like that. Luckily he had been patrolling, or else, what would happen?

Without saying a word, Tajima picked the poor kid up. Madara didn't protest, even though on normal days, he hated being carried like a child. But for the first time ever, he noticed his father's smell: cracking fire on winter night, and he was family. So the young Uchiha just drifted off to dreamland, he was safe.

The heat lasted 3 days, 3 days in and out of consciousness, tearing clothes and clawing his own itchy skin. It was hot, like fire burning inside of him. Sticky liquid, no matter what it was, seeped through his pants and made his toes curl. Most of the time, Madara's ears blared with chants and hammer sounds that made no sense. He covered his ears, wanting nothing more than to bang his head against the brick wall.

When those sounds didn't torture him, he could cracked his eyes open and be aware of his surroundings. Madara heard Izuna's voice, loud and furious, demanding to see him and another calm voice telling his younger brother 'No'. That voice belonged to his father and the man would come in everyday to bring him food.

"What do I do know?" Madara whispered weakly.

It was the morning after the 3rd day and his mind was much clearer. Madara felt dirty, probably from sweating and the lack of bath for 3 days straight. His limbs felt like noodle too.

Without the heat, the boy also noticed that his sense of smell had improved dramatically. It was nowhere near an Inuzuka, but still. He could smell his father's scent, something he had just been able to do since the heat started that day in the wood, and his incense-liked scent which marked him an Omega.

"Does everyone know?"

Tajima shook his head:

"No, and I will make sure no one will."

"How?"

Madara questioned. If what he knew were true, any adult would be able to sense him know. How was his father going to trick the whole clan about his secondary gender?

Tajima handed him a small bottle. The boy gingerly opened then quickly screwed shut when smoky scent hit his nose. Was that supposed to be Alpha pheromone? He didn't like it, at all.

"Apply that thing to your scent gland twice a day…"

Tajima tapped his son's neck.

"…and you would be fine."

With that, he left the room.

Author's note
So... Omegaverse... Can't say that I am not nervous writing this. The whole A/B/O concept kinda went over my head at first. You can find a Tumblr's post that explains it clearly; I'll only add a few details for my verse:

1. Male Omegas are rare, and as they are said to be able to give birth to the strongest of offspring (which we call pups), they are extremely sought-after.
2. Usually, only Alphas are to become Clan leader, due to obvious reasons. There are cases that Betas take the lead, but they are often challenged by the other gender. Omegas are out of question, they are not even allowed to fight (yet).
3. Pups cannot sense others, or have unique scent of their own. This changes when puberty hits, however, and each gender has different scents:

Alphas often smell pungent or bitter, although some can be mellow.
Betas don't smell much, quite bland, infact or just not smell at all.
Omegas' scent is sweet and the closer they are to the heat, the more alluring they smell