A/N: This is my first really long fic for Naruto. Naturally, it's about someone from Otogakure. (Major Oto fangirl.) Obviously, it's about Sakon and Ukon, from their birth onwards. Things get progressively more messed up for them. Ho hum.

There will be quite a few OCs in this fic, due to necessity. For example, we don't know who Sakon and Ukon's parents are, so I had to make them up. But this fic is still starring Sakon and Ukon (more so when they get old enough to talk, heh), and there's not going to be any weird OC pairings, so don't worry about that.

I'm going to try, at least for a while, to write each chapter like its own story. That way if I get writer's block, I won't leave a cliffhanger.

Disclaimer: Kishimoto owns Sakon, Ukon, their kekkei genkai, the Naruto world, and many fangirls' souls. I own Futago, Futan, Akusei, Dokusei, Mizuiri, the Shinken clan, and many less souls.

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Thicker Than Water

Identical Defect

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The Shinken clan was in an uproar over the birth of its latest twins. It was utterly shameful. This would never have happened if Futago hadn't married Mizuiri, who didn't even have a sister, much less a twin of her own. A shame, a terrible shame.

It had been years since something like this had happened. The last crisis had been some thirty-five years back, before Futago and his twin Futan had even been born. There was a poor little girl who had been born without a sister. This current crisis certainly wasn't as terrible, but Futago would never live this down. Mizuiri, not originally part of the clan, naturally had no idea what was wrong and was simply proud to have birthed two beautiful, healthy boys. And there lay the problem.

They were both equally beautiful. They were both equally healthy. They were both, in every way possible, completely identical twins. They certainly didn't look to be Shinken twins, though the doctors had said they possessed the clan's kekkei genkai – there was a bit of relief. Still, something had to be done about this problem, the fact that the twins were both healthy.

Which is why the Shinken elders had decided to pay a visit to Futago and Mizuiri.

Several days after the birth of the twins, Akusei knocked on the door of Futago's home, and stepped back to wait for a response. In a moment, a man opened the door. He was gaunt, pale, and shivering, eyes unfocused and mousy brown hair dangling limply around his face. He hunched forward in a slight bow and stepped back to let Akusei in.

Without bowing back, Akusei walked in and slipped his shoes off. "Futan. Where is Futago-san?"

Rather than answering, Futan turned and shuffled down a hall. Apparently, he'd been instructed to let their visitor in. Akusei followed until they reached an open room with a view of the garden in the back. Futago was already seated. He had been expecting a guest.

"Futago-san, it's good to see you." Akusei bowed slightly to Futago.

Futago looked up with a sharp gaze, and smiled slightly. He bent forward from where he sat to return the bow. "It's good to see you as well, Akusei-sama," he said as his twin crouched behind him and slipped back into his body. Futago looked like a much healthier version of his brother; he was wiry and strong, fair-skinned, with light brown hair neatly framing his face. "I've been waiting for someone to come any day now."

Akusei sat across from Futago. "The elders have been discussing what to do with your children. We didn't want to get you involved until we came to a decision."

"I see," Futago said. He appeared tense, worried. "It won't be as bad as before, will it?"

He was referring to the girl who had been born alone, thirty-five years ago. The clan didn't have the resources to raise a child who wouldn't be able to utilize their kekkei genkai, but putting her up for adoption in the village would have given outsiders a chance to learn the secrets of the Shinken's bloodline. She had been put to death.

"No, no, of course not," Akusei said. Futago simply nodded, but Akusei heard Futan sigh with relief. From Akusei's back, his twin Dokusei laughed, a quiet wheezing.

Futago was one of the most stolid, unemotional members of the clan, but his twin was quite a different story. Akusei remembered once when Futago was a child he'd gone with a few friends to watch a tragic play. Futago had sat like a statue through the whole performance, except towards the end when he kept passing tissues over his shoulder to his sobbing brother.

"You've come up with an arrangement, then?" Futago asked.

"We have," Akusei said. "We decided that it would be best to treat them as if they were any other set of Shinken twins. I think it will be easier for everyone, especially them."

Futago frowned. "I'm sorry, but how would that work? They're almost identical, not like our normal twins."

Akusei nodded. "We've taken this into account, Futago-san. Don't worry."

"I'm sorry, Akusei-sama. Please, go on."

Normal Shinken twins were not born equal. One always came out a healthy, strong baby, and the other was frail and sickly from the start. From its first days of life, the sickly twin was placed inside its healthier sibling, and they learned to live together. When the twins grew older, the healthy, dominant one was admitted as a member of the Shinken clan and began training as a ninja. The inferior one lived inside its twin, to be used as a tool in battle and in daily life.

Of course, this was a little tricky when the twins were identical.

"One of the twins will be put inside the other, as usual," Akusei said. "Within a few years his muscles will begin to atrophy, correct?"

Futago nodded slowly. "That's true…"

"In that case, before long he will be considerably weaker than his brother," Akusei said. "By the time they are toddlers one will be dominant and one will be inferior. It will be as if they were born that way."

"I see. It makes sense," Futago said. "But are the elders certain the inferior will atrophy properly?"

"No, we aren't," Akusei said. "However, our only alternative is to give one of them surgery, to make him weaker. That's the surest way to solve the problem."

"Mizuiri would never accept that," Futago said with an apologetic smile.

"I know," Akusei said. Mizuiri was not part of the Shinken. She didn't understand the measures an advanced clan had to take to preserve a kekkei genkai.

"We will accept your first offer," Futago said.

Akusei nodded and stood. "Would you like to take some time to think about which twin you would like to be dominant?"

"No, it's best to do this now," Futago said, standing as well. He turned and left the room. "The twins are this way."

Mizuiri had just finished bathing the twins and was dressing them again when she heard footsteps in the hall. She glanced up as the four men – she refused to think of them as only two men, they had their twins with them after all – walked into the room.

"I take it you've come up with a solution?" she said warily, brushing a few strands of blue hair out of her face. She was clearly not Shinken in appearance, even ignoring the fact that she had no twin. Mizuiri had light, almost dusty blue eyes and hair, whereas the Shinken had black eyes and universally brown hair. The twins had already inherited their father's eyes. Mizuiri hoped they'd at least get her hair.

Akusei glanced at Futago, allowing him to give the news to his wife. He stepped closer and put one hand on her shoulder as he spoke to her. "We've decided to treat them like other Shinken twins. We'll place one in the other and let them grow like that."

Mizuiri didn't meet Futago's eyes. "I thought you might," she said. "I never thought I'd marry into a clan where being born healthy is a birth defect."

Futago winced. "Mizuiri, don't think of it like that," he said. "You knew about our kekkei genkai when we married. You understood what it would mean if we had children."

"I could have handled raising a sick child!" Mizuiri said. "I didn't think I'd have to help make him sick."

"Mizu-chan…" Futago reached up to stroke Mizuiri's cheek, and she knocked his hand away.

"Don't you Mizu-chan me!" Mizuiri snapped. "We are not school children anymore, Futago! These are your sons. Can you do this to one of them?"

"I'd be an irresponsible parent if I didn't," Futago said.

Mizuiri glared at him. "I can't argue with you, can I?" she said. "Fine. Do what you have to. But you won't have my support."

"I'm sorry," Futago said. "Mizuiri, would you like to choose which one of them will be dominant?"

"Don't make a mother choose between her children," she said. She crossed her arms, taking a few steps back, far enough to allow Futago to work but close enough to protect her babies.

Futago looked at his children, uncertain. They were lying beside each other in their crib, damp from their bath, squirming slightly, and they still looked identical.

"Are you having trouble deciding?" Akusei asked, stepping up beside Futago.

"This is harder than I thought it would be," Futago confessed.

Akusei nodded. "What are their names?"

"Ukon and Sakon," Futago said. Named for the two connected sticks of a nunchaku, Left and Right.

"Strong names," Akusei said approvingly. "But is the right hand not usually dominant to the left hand?"

Futago considered this advice. Right is stronger than Left, so Sakon would be stronger than Ukon. "I understand," he said. "Futan?"

Futan silently slipped out of his brother and stood beside him. "You take Ukon," Futago said, pointing to the child on the left.

"Yes," Futan said, barely a whisper, lifting up Ukon enough to undress him but being careful enough to hold him low in the crib, so if his trembling grip slipped Ukon would not fall. Mizuiri noticed this.

Futago only had to take off Sakon's shirt. He placed his hand on Sakon's back, channeling in a bit of chakra to his spine. Activating Shinken siblings' kekkei genkai the first time required some effort, but it became easier after that.

Meanwhile, Futan was struggling to channel chakra through Ukon's entire body. He wasn't trained in ninjutsu the way his brother was, and he also had a much larger area to cover. Finally, he exhaled softly. "Ready."

Futago nodded, and held Sakon face down. Futan lifted Ukon over him, placing his feet first on Sakon's back, and as his feet started to slide him he slowly pushed Ukon down into Sakon. Mizuiri stood to the side, biting her thumb until it bled to keep herself from demanding her husband to stop. As bad as this was, if she refused to go through with it then they might do something even worse to her children.

Ukon and Sakon slid together without a sound, only wiggling a little bit the way babies do. But when Ukon was almost fully inside Sakon and only his shoulders were poking out, he suddenly reached out with one hand and grabbed Futan's left thumb.

Futan froze. Even his trembling stopped. He stared directly into Ukon's eyes as Ukon squeezed his thumb.

"I'm sorry, nephew," Futan whispered. Futago gave his brother a quick, bewildered look. Never before had Futan spoken when it wasn't necessary.

Quickly, Futan shook Ukon's hand off his thumb and pushed him the rest of the way into his brother's body. Ukon looked around calmly at the outside world, not at all bothered by the fact that he was now just a head sticking out of Sakon's back.

Futago set Sakon down in the crib, sitting upright, and dressed him. He was sure to leave the collar of his shirt wide open so it wouldn't choke Ukon. "We're finished," Futago said as Futan slipped into his back again.

Mizuiri nodded tightly, now biting her other thumb and trying not to cry. A ninja must not show emotions under any circumstance, even for the sake of her children.

Futago couldn't think of any words of comfort, so he turned to Akusei. "Thank you for your help, Akusei-sama. I'll show you out," he said.

As they walked away, Futan lifted his head and gazed directly into Mizuiri's eyes. He cried for her.

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Mizuiri had never slept in the same bed as Futago for a full night. They had tried early on in their marriage, but Mizuiri hated having to share the bed with her brother-in-law and Futan was too weak to spend an entire night in a bed by himself. So she'd slept in her own bed. When the twins were born, it had been easy for her to move into their room so she could care for them at night. It also allowed her some degree of privacy with them.

This could all be very useful.

The first night the twins were connected, Mizuiri sat up for hours, getting used to cradling them in her arms without covering one of their faces with her arm. She'd have to go to other Shinken mothers tomorrow and ask them how they did it.

A soft knock came at the door. "Come in," Mizuiri called, expecting Futago to come in. To her surprise, it was Futan – unless Futago had lost twenty pounds and developed Parkinson's disease in the last few hours. "Futan-san?"

"Yes," Futan said softly, walking unsteadily to Mizuiri's bed and sitting heavily beside her. "I need to talk."

"That's fine," Mizuiri said. "I'm listening. What is it?"

He took a moment to catch his breath, and then looked at Ukon and Sakon in Mizuiri's arms. "He doesn't have to be like me," Futan finally said. "They were both born like Futago."

Mizuiri stared at Futan. He had never said this much at one time, as far as she knew. "I… Thank you, Futan," she said. A lump formed in her throat. She imagined Ukon one day, feeble like Futan. Could she still prevent that?

Without a word, Futan reached forward and placed his hand between Ukon and Sakon's heads. He pressed his fingers to where their spines met, and carefully lifted Ukon's head. Ukon slid easily out of Sakon's back until both twins were separate. "An old trick to draw a Shinken from another's body," Futan explained. "Lift them from the spine and they come out."

"I'll remember that," Mizuiri said, looking at her children.

Futan stood unsteadily, and Mizuiri automatically reached out with her left hand to help him to his feet. "If they sleep separately at night, Ukon might not get too weak," Futan said. "It will just take a little chakra now to put Ukon back inside Sakon each morning."

Mizuiri nodded. The lump was now large enough that she didn't think she could speak around it without crying.

Futan shuffled to the door, saying, "I have to get back before Futago wakes and finds out I'm missing." He shut the door behind himself.

Cradling Sakon and Ukon in one arm each, Mizuiri stood up and placed them in their crib on opposite ends. As she was walking back to her own bed, she heard a loud thump in the hallway.

Mizuiri hurried outside to help Futan to his feet and guide him back to Futago's bedroom. Meanwhile, Sakon and Ukon slept, peacefully and separately.

Until Sakon needed his diaper changed at three in the morning.

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A/N: I know there are some people obsessed with looking up the meanings of character names, myself being one of them, so for those who care: Futago means "twin" and Futan means "a burden" (poor Futan). Akusei means "malignant cancer" and Dokusei means "toxicity." Mizuiri's name comes from mizuiro, which means "light blue." Shinken is the surname of the man who helped save the Kobudo martial arts, which is where the nunchaku comes from, and a shinken is also a kind of Japanese sword.

Please review! The hits counter might tell me how many people clicked on my story, but they don't tell me whether or not anyone read past the first paragraph. If you read this far, please let me know. Praise makes me squee, concrit makes me write better, and flames make me laugh. Let me know what you think!