Notes: I would like to thank you all for your support. The reviews you've left have been very special and I'm very happy to know that you've enjoyed these little scribbles! I wish there were some way to thank you individually, but I guess this will have to do. Thank you! So: the plan for this one was to use Tobirama to explain my headcanon for sensors and how their skills work, but I ended up not talking much about it at all because Hashirama took over and Tobirama is so young that he doesn't quite understand it himself. Oh well...
Summary: Tobirama finds out he's a sensor.

Dependence

It was a hot summer afternoon and Hashirama found himself in the unfortunate position of having to train outdoors. There was not a breeze to be felt and the air was so muggy that every article of clothing stuck to his skin.

Given the exercise that his father had set up for him and Tobirama, it might have been an advantage, were it not for the long hours that they had to spend in the sun. The two boys were to sit, immobile, and meditate, focusing their chakra to hold a leaf against their forehead.

The leaf stayed in place easily enough – even had he not been using chakra, Hashirama doubted that it would go anywhere – but sitting still was torture. Hashirama was cooking in his clothes and the sun was burning the skin of his exposed arms and shoulders. He could not wait to be dismissed so that he could go swim in the river that crossed the Senju encampment, take refuge indoors or just sleep off the time until the weather was not quite so hellish.

He opened his eyes the slightest fraction to look at how Tobirama was doing next to him. His younger brother was sweating as much as him, his untrimmed white hair appearing darker at the tips where it stuck to his neck and forehead. Unlike him, though, the heat did not seem to trouble him. He looked very at ease, expression bland, betraying no exertion or discomfort. He was perfectly at peace.

A sudden sharp finger flick to his shoulder had Hashirama closing his eyes and focusing back on the exercise, however. Butsuma was nearby, monitoring the boys' progress, and no doubt had noticed his distraction.

He tried to think about anything other than how hot it was: how much longer father would keep him and Tobirama there, if there would be anything special for dinner, if mother would let him take Kawarama out to go look for that dog he had seen wandering around the other day… He thought that his younger brother would like to see it. The dog had not been very big and had had a few missing patches of fur on its flanks, but it had been friendly and Hashirama did not think that Kawarama had ever petted one. Perhaps they could just go for a swim…

"All right, boys. That's enough. We'll continue tomorrow."

Butsuma's voice was music to Hashirama's ears. He wasted no time in brushing the stupid leaf off of his forehead and jumping to his feet.

Tobirama was not as quick to react. His brother had yet to so much as open his eyes. Had he not heard father's dismissal?

Impatience getting the better of him, Hashirama shoved him on the shoulder to get his attention, but even that did not have the intended effect. Tobirama opened his eyes only sluggishly and gave him a blank look.

"Come on, Tobi!" he urged. "Let's get out of here and go do something fun!"

Before Tobirama had the time to say anything, Hashirama had grabbed him under one arm and pulled him to his feet.

He was expecting his younger brother to wake up and share his enthusiasm that they were free for the rest of the afternoon – a rare event, given their gruelling training schedule – but, instead, Tobirama remained listless, sleepy, leaning almost his entire weight against Hashirama's side. He was so unsteady, so clearly out of it, that he would have fallen right back down otherwise.

Hashirama found it amusing when he tried to get Tobirama moving and he stumbled on his own feet. Perhaps his brother had "meditated" a little more thoroughly than their father had intended. With their early practice rounds, none of the boys had been having enough rest lately. It was only natural for Tobirama to use the opportunity to catch up on his sleep.

When he looked closer, however, he realised that Tobirama was pale – much paler than usual. His skin was clammy. It was not just his hair that was sticking to his skin – his clothes also had wet patches down the back and in the armpits. Their father believed that being able to endure the full force of the sun for a short while was part of the bare minimum abilities that any human being should possess, let alone a shinobi, but the truth was that Tobirama had always been vulnerable to excessive heat.

He started to worry that something was not quite right with him.

"Tobi?"

Hashirama grabbed him to make sure that he did not fall and wondered if he should help his brother sit back down or wait for him to snap out of whatever he was going through at the moment. Tobirama had probably just gotten up too fast, the older boy reasoned.

Seeing that his sons were not leaving when usually they would have already been specks on the horizon, Butsuma stopped to take a closer look at Tobirama himself.

"What's wrong with him?" he asked.

Hashirama had no idea and told his father just that. "I guess he's just tired and the weather's too hot?" He wanted to ask Tobirama next if he was feeling better, but he never had the chance.

The younger boy's head tilted forward dangerously. It was the only warning sign any of them had before he collapsed, unconscious.

"Tobi!"

Hashirama felt his brother's arm drag down the side of his body. He tried to go down with him, to hold him, but he was just a beat too late and not strong enough to hold so much dead weight. Tobirama's head hit the ground freely. There would be a nasty bump there when he woke up… if he woke up.

For a moment, all that Hashirama could do was stare at his brother splayed on the ground, too afraid that he would make things worse if he touched him. It was Butsuma who rushed over and pushed the panicking boy away to tend to his fallen son.

Hashirama watched his father kneel down to examine Tobirama, checking his temperature and feeling the back of his head where he had hit the ground for any signs of blood. Hashirama wondered if he should go get water or bandages, but he was so worried that he did not want to let his brother out of his sight. What if he was not there anymore when he got back?

After a few seconds, however, his father took action. Picking up Tobirama as if he weighed nothing – and, for someone who wore dozens of kilos in armour on a daily basis, it probably felt that way –, he prepared to run out of the training grounds.

Hashirama tried to follow, but Butsuma put a hand on his shoulder and barked at him to stay put. If at first Hashirama did as he was told, his obedience vanished the moment that his father was out of sight. Making use of all the tracking techniques that he had been taught, he followed him all the way to the stream that crossed the Senju encampment and hid behind a tree, straining his neck to catch a glimpse of his brother.

Butsuma did not even pause to remove his armour. He just waded into the water with Tobirama. Supporting his son's head on the crook of one arm, he submerged his body and used his free hand to splash water on his face.

The river was not very deep, but its currents were strong and Butsuma had to turn back towards the river bank while he found his footing and adjusted his hold of Tobirama. Already frightened, Hashirama was even more perturbed to see that his father's eternal scowl had given way to an altogether different expression. Hashirama almost could not believe what his eyes were telling him, but his father looked nervous, lips pursed and eyes widened just that little bit more than usual.

Hashirama had never seen him be anything other than a ruthless, unyielding rock and now here he was, treating Tobirama like the fragile child that he was, stroking his cheeks and smoothing back his wet hair.

Before Hashirama could quite get used to the idea, Tobirama's eyes opened.

"Father… What… Where am I?…"

It broke Hashirama's heart that his brother sounded so lost. What was wrong with him? Would he recover fully or would this happen again the next time they had to practice?

He felt so guilty.

Unaware of the conflict within his other son's heart, Butsuma shushed Tobirama and put a hand over his forehead to check for a temperature.

"Father…?"

Hashirama almost did not hear his brother's voice, so raspy it was. In contrast, Butsuma's carried loud and clear:

"Are you feeling better, Tobirama?"

"Yes… I think… What happened?"

"You fainted."

"Oh…"

Hashirama's spirits lifted. His brother was awake and responding! He wanted so badly to go to him now, but he was still under orders from his father not to. And if there was one thing he knew, that was that he should never contradict his father.

"Are you dizzy?" Butsuma inquired. "Lightheaded?"

"I don't think so…"

Butsuma sighed and began to wade out of the water, only letting go of his young son when he reached the shore, to lay him down over the grass.

Knowing how his father despised idleness, the young boy immediately tried to get up, but this was one time Butsuma broke his own rules. With a scold on his lips, their father ordered Tobirama not to move. And then he called out:

"Hashirama! If you're going to stand there you might as well make yourself useful. Run down to the house and get your brother a towel and a change of clothes!"

Hashirama was startled. He had been so sure of his hiding place.

"Y-Yes, father," he said, nonetheless. The thought of letting his brother out of his sight gutted him, but he had already disobeyed his father once and he dare not push his luck by doing it a second time.

He ran as fast as he could. His mother, busy weaving fabric on the loom, looked up when he came into the house without stopping to take off his sandals.

"Hashirama?" she called. "Did something happen?"

Hashirama's mind was such a whirlwind that he did not even hear her question. He entered the bedroom and grabbed the first thing he found before leaving as fast as he had came, with not a thought to spare to closing wardrobe or bedroom doors.

Kawarama, playing in the main room, put down his toys to look at his big brother in surprise. He tried to call his name, but he was as ignored as his mother before him.

The one thing that Hashirama focused on was sprinting back to the river, his heart in his throat. What if something went wrong and Tobirama fainted again? It was only when he got there and saw that his brother was sitting up on his own that he was able to relax.

But the mood was different now than when he had left. Tobirama was looking down at his hands and Butsuma was standing a little ways off, back to his usual, distant self.

Hashirama dropped to his knees next to his brother, still holding on to the clothes.

"Are you okay, Tobi?"

Tobirama slowly turned to look at him. His movements felt awkward to Hashirama, jerky. He had a little more colour on his cheeks, which was reassuring, but he still did not look at all healthy.

"Yes, big brother," he said, then winced.

Butsuma brusquely took the clothes from Hashirama's arms.

"Go home, Hashirama. Tell your mother to start dinner. Tobirama and I will be there shortly."

Hashirama did not want to leave again, but his father pulled him up by the back of his shirt and shoved him in the direction of the house.

"GO!" he roared.

Hashirama was torn. On any other day, it would not have so much as crossed his mind to not listen to his father when he yelled like that, but Tobirama needed him. In the end, though, it was Tobirama himself who put an end to his indecision:

"Please, big brother. I'm better now, but you're making it worse by being here… Please go."

The words gutted Hashirama. Making it worse? Yes, he had made him stand up before, but he knew better than to do it again. How could his brother think so little of him…

But who was he to argue? He had done his brother wrong, so the least he could do was submit to his requests now.

Hashirama returned to the house as slowly as possible, constantly looking over his shoulder to check if his father and Tobirama were joining him. His mother asked him why he had been running before, but Hashirama was still so very distracted that he could not say much. He told her that Tobirama had not felt well after training and passed on Butsuma's message, before absently sitting down next to Kawarama on the living room floor.

Kawarama did his best to get his brother's attention, but when he realised that he was not about to get a playmate anytime soon, he became all the more invested in making his game extra interesting to entice Hashirama.

It was not until the whole family had gathered at the dinner table almost one hour later that Hashirama saw his brother and father again. Butsuma looked a little dishevelled – his clothes had dried but they were ruined from going into the water – and Tobirama thankfully appeared like he was back to normal.

They took their places at the table: Butsuma at the top, next to his brother, his elderly mother and a pair of cousins who acted as his advisors in the clan; and Tobirama in between Hashirama and Kawarama further down.

As always, Kawarama's excitement to see his brother was overwhelming. He would have leapt from the table to hug him if Hashirama had not stopped him.

Tobirama might look like he was better now, but Hashirama was not taking any chances.

"Kawa, stop that! We're at the table. Leave Tobi alone!"

Kawarama pouted at him and looked like he was going to protest, but it was Tobirama himself that soothed him.

"It's all right, Kawarama. Big brother is right."

Hashirama addressed Tobirama then:

"Tobi? Are you okay?"

Tobirama smiled.

"It was nothing, big brother. I'm fine now. Father helped."

"What happened?" Hashirama needed to know. Relief had opened the floodgates of all the anxiety he had been holding back. "One minute you were fine, the next you were falling right in front of me! Are you sure you're okay?"

"Yes, big brother. I'm fine now," Tobirama repeated.

"I was so worried…"

"Father says that I meditated too deeply."

Hashirama grabbed on to the new piece of information.

"Too deeply? What does that mean? He's always saying that we're not doing it right and to focus more and to try harder…"

Hashirama quietened before his annoyance with his father could get in the way of his concern for Tobirama. His brother looked a little shy now.

"He says that it's different with me, only he never realised it."

"Huh? Different how?"

"It's… It doesn't matter."

"But you're better now, right?"

Tobirama was a little more confident about answering this time: "Yes, I'm fine."

The tension finally left Hashirama's body.

"I'm so glad… Did father say if you can keep training with me?"

"I think so. Yes."

"Good!" Hashirama's excitement was contagious. Tobirama nodded, looking as relieved as he did to be allowed to remain in his big brother's company.

Dinner went the same as usual, with the boys keeping silent while the adults talked. Their mother had opened the doors that led to the house's inner garden and they could all hear the late afternoon breeze playing with the wind chimes that hung on the porch.

Butsuma and his advisors discussed the current state of the clan and the boys' uncle, Akira Senju, shared the latest information about the movements of the other clans that he had learned from the surrounding farms and settlements. Akira was a couple of years older than Butsuma, but a run in against a Hagoromo ninja in his youth who had been a little more creative in his use of exploding tags than expected had cost him a leg and part of an arm and so the leadership of the clan had passed on to Butsuma, while he had been left with managing the Senju's intelligence network.

Hashirama listened attentively while keeping an eye on Tobirama, to be sure that he would not faint again. Meanwhile, Kawarama played with his food and pushed the things that he did not like onto Tobirama's plate. Tobirama snuck Kawarama's favourites into his own plate in return.

Later that night, after the visitors were gone and the boys had settled down to sleep in their shared bedroom, Hashirama remembered something.

"Tobi? You awake?"

"Mmm?" He grunted, obviously having been close to sleep. "What is it, brother?"

"Do you remember when we were back at the river?"

"Yeah…?"

"You said that my being there was making you worse. What did you mean by that?"

Tobirama took a moment to reply.

"Does it matter? Let's just rest, Hashirama… Father won't go any easier on us in practice tomorrow than he did today."

"No. I want to know. Why did you say that?"

Tobirama sighed. The room was quiet for a moment before Hashirama heard his brother shift in his mattress, rolling until he was on his side facing him.

"Sometimes…" he started hesitantly, "when you're close, it feels like there's this pull… It's hard to explain, but it's like…" He stopped himself. Hashirama kept quiet, giving him whatever time he needed to gather his thoughts. "It's like… like your heart's beating for the both of us."

The words made no sense to Hashirama. It was only a week since his father had taught him and Tobirama about how the human circulatory system worked. Tobirama had been fascinated, but Hashirama had retained only the bare essentials, such as the location of the main arteries and veins, the best places to cut into with a sword and what to do if one was stabbed. He wondered if perhaps Tobirama was talking about something from that lesson.

"What do you mean, Tobi?"

"It doesn't happen all the time. At least not anymore. I think it must be because of the training. I used to feel it all the time before."

"Feel what?" He was getting impatient and forgot to whisper. He regretted it at once, when he heard Kawarama shift somewhere in the darkness. Their bedroom was tiny and all the boys slept a mere arm's length from each other. Both Hashirama and Tobirama waited to find out if the younger boy had woken, but thankfully he had not.

"I always used to know where you were because something inside me would pull me towards you… I don't know what to call it… It's like a sixth sense. Yeah… a sixth sense. Just like you can use your eyes to see what's in front of you or your ears to listen to what's around you, this sixth sense told me where you and everybody else was at any time. I just had to stay still and search for that pull."

It was a confusing notion to young Hashirama. He had never felt anything like what Tobirama described. When he needed to find anyone, he had to go look for them, search every room and every place he could think of until he came upon them. It was true that his brother had always been uncannily adept at finding him whenever he wanted, but how could that be done by staying still? His brother did not have a second set of ears or eyes, either, so what was he using for this so-called sixth sense? What he was saying made no sense, but he knew better than to question whether Tobirama was telling the truth or not. His brother had never been one to lie or exaggerate such things.

"How did you do it, Tobi?"

"Father says that it's because of how my chakra pathways are arranged. I just did it. Lately, though, it's gotten harder to do. When I close my eyes like usual, the pull is still there but it's too faint to follow."

"I see." He did not. "But what does that have to do with you passing out today?"

"I felt that pull really strongly today, while we were meditating. It was wonderful. I could just follow it until it felt like my whole body was vibrating with it. It wasn't like when you hold your hand close to fire and feel its warmth. It was like the flame was inside me and I felt it with the whole of my skin and my insides too. Or… think of that pull as a wave in the sea. If I stand in the middle of the water, I can feel the wave brush my legs. I can tell where it is and which side it came from. But today it was like I had actually become a part of the water again and was mixed in with the wave. It was like being carried away in a dream you can't control."

The conversation was becoming more and more confusing. Hashirama was not sure that he could follow what his brother was saying. It sounded a little like madness to him.

"Did you tell father about this?"

Because if anyone could understand what Tobirama was talking about, that would be Butsuma.

"Yes," Tobirama confirmed. "He said that I'm a natural sensor. Something about ninshuu, but he didn't explain."

Hashirama knew the term. His father had explained to him about the various ways that one could utilise chakra and how the ninja arts that they practiced had evolved from an older form of chakra manipulation called ninshuu that had been invented by the legendary Sage of the Six Paths.

Sensing was one among the many techniques of ninjutsu. Hashirama was even due to learn how to do it when he got older. He had just never tried to imagine what it would actually feel like to sense something with chakra.

"That's amazing, Tobi! You must be really talented!"

Tobirama hummed in response. Hashirama was so proud of him that he almost forgot to keep his voice down again.

"But if you've always been able to do it, then why did it make you faint today?"

"Father said that I was meditating too deeply and focused too much on your presence next to me. He said that your chakra is so much stronger than mine that it unbalanced me. I should have waited a while after the meditation was over to give my chakra enough time to go back to normal."

Hashirama wasn't sure about what he meant by stronger chakra, but one thing he did know. He had been the one to rush Tobirama before he had been prepared.

"I'm the one who made you get up… I'm sorry, Tobi… I didn't realise what would happen…"

"That's all right, brother. I'm fine now. Father helped."

But that did not ease Hashirama's guilt.

"I am so sorry… I won't ever do it again."

"It's fine."

Hashirama waited a moment. The guilt about having caused his brother distress would forever remain with him. The thing that he wanted most in the world was to keep his family safe and now he had caused Tobirama pain without realising it. He had made him lose his balance – whatever that meant – and then had compounded the mistake by forcing him to his feet before he was ready. It was a double fault.

But there was something else that he was curious about too.

"Can you still feel it now? The pull, I mean?"

"Yes," Tobirama said. "I can feel you and Kawarama, mother and father in the next room, our uncle and grandmother and the rest of our clan in the houses around ours."

"You can feel things that are that far away?"

"They're just an impression, really. Out of all of them, your presence is the strongest, big brother."

"Because I'm right next to you?"

"No. Your presence is different from everyone else's. It's so much brighter… It's warm, too. It reminds me of the sun. With the others, I can feel their chakra pulsing when I'm sensing them like this, but in your case, it goes deeper than that. It's like my chakra wants to imitate yours and it makes my heart beat in tandem with it. It's… strange, but at the same time, it's a good feeling because I know it's you and it means you're close."

Hashirama smiled. He still did not understand everything and it all sounded very weird and very concerning to him, but if Tobirama said that he was all right with it, then so was he.

"I was so scared, Tobi… You looked like you were dead."

"…I'm sorry, brother. It won't happen again."

"No, it won't," Hashirama agreed. I won't let it, he added in his head. "Let's go to sleep now, okay?"

Hashirama heard Tobirama hum again in agreement. "Good night, brother," he said before rolling back to lay on his other side, facing away from his brother.

Hashirama was still too awake to follow his example. Even though he knew he needed his rest and would regret not sleeping as much when Butsuma was pushing him hard the next day, he could not bring himself to let Tobirama out of his sight just yet.

He would make sure that nothing like the events of this day ever happened again. He would be more careful. He never wanted to hurt one of his brothers again.

"I promise, Tobi."

He fell asleep to the nocturnal calls of crickets and to the sound of his brothers' gentle breaths.