"I am rather certain it does not have to be this difficult, captain Yamato."
"I am rather certain you don't have to talk this much..."
"My apologies, but I do believe it really was not necessary to take this route."
"No~? Really!? I hadn't noticed yet..."
"Oh, my apologies. I thought I had made it clear—"
"That was meant sarcastically Sai..."
"Oh... Does that mean you are annoyed with me? I read in this book—"
"Shut up. Now."
"Yes captain Yamato."

The two were half-way up a steep cliff that was almost impossible to climb, even with the aid of chakra. They were on a mission to keep an eye on Yakushi Kabuto, who had only become more dangerous after his boss Orochimaru had been defeated. Originally, their team had also included Anko Mitarashi, but when Yamato had used his authority as team captain to decide they were going to take a safer and apparently more difficult route, Anko had used her authority as a woman to stay exactly where she was and eat dango.
Sai, on the other hand, had followed his captain as the obedient little subordinate he was. Now he regretted that decision, or rather, he believed that Yamato's choice might have decreased their chance of successfully completing the mission. Regret was still a somewhat alien concept to the Root member. Of course, Yamato himself did regret the decision. He would rather die than admit it, though. Except, maybe, if his Kakashi-senpai was here. He'd do anything for him.

However, Kakashi was all the way back in Konoha and he was stuck here with a boy that lacked any true understanding of how to interact with other people. Even his infamous Face of Terror was useless against Sai. "The Hokage be damned, I should never have accepted this mission..."
"Did you say something captain Yamato?"
"I said it would be a good idea to make camp when we get to the top."
"It is getting dark already. I guess you can have good ideas after all." Sai smiled one of his fake smiles, although it was much more sincere than the ones from before the Tenchi Bridge mission. It didn't impress Yamato, though. "One more word and I'm pushing you off this cliff, Sai."
"I believe that would be tantamount to treason and attempted murder, captain—"
"Shut! Up!"
"Yes captain Yamato."

Finally, after a climb that took most of the day, they reached the top of the cliff. Yamato was exhausted, not so much by the climb, as by Sai. He could barely grow an adequate house to use as a camp site. Still, he managed, creating a nice little abode with the Konoha crest displayed proudly above the entrance.
Supper was quick and simple, as it always was on such missions. It was adequate, but not very satisfying. Not that it would had mattered if it had been, as Yamato was far too stressed out to enjoy it. This mission was not going as he had planned. Luckily, Yamato had discovered a hot-water spring just outside the house, so he could create a nice onsen after supper and finally let some of the tension leave his body. Also, Sai was still silent.

The water was perfect, simply perfect. It had nice and hot and the subtle smell of minerals relaxed both the poor captain's body and mind. He sank away in an almost meditative state of mind, and he was certain he would have reached Nirvana if it hadn't been for Sai sitting opposite of him, slouching slightly in an almost perverse sham of enjoyment. Yamato wondered if Sai was even capable of really enjoying something and what was going through the boy's mind right now. He stared at the boy for a while, musing on these thoughts, when Sai's voice suddenly broke his concentration.

"Captain Yamato? Could I ask you something?"
"Must you?"
"It is rather important, I think..."
Yamato sighed deeply. "Ask away then."
"What is it like to have a boner?"
"What?!" Yamato sat up in shock, glad that the blush he had from the heat was covering up the blush he now had from embarrassment. "Why would you ask that?"
"Because you have one."
Yamato's eyes grew wild and he quickly looked down, only to be greeted by his member standing at full attention. "Fuck!"
He quickly put his hands down to cover himself up. "I... That... Ehm..."
"Is something wrong captain Yamato?"
"Eh? I... Well..." Yamato slowly realised how ridiculous he was being. There was absolutely no reason for him to be acting like a little boy caught masturbating. Sure, it was a little embarrassing, but he could appreciate the humour of the situation. Yamato chuckled and turned his attention back to Sai. "Nothing's wrong Sai, except for you not knowing what it's like to be hard. And you using the word boner... Don't tell me you never had a hard-on before."
Sai thought for a while. "I guess biologically speaking I have to have had bo— hard-ons, but I cannot remember ever having had one and I certainly cannot remember what it was like to have one."
"It's official now... Root's training is a crime against humanity..."
"What do you mean? Is that hyperbole?"
"I'm ignoring that last question and I mean that every guy should know what an erection is like. it's pretty much essential to manhood."
"So I am not really considered a man without this knowledge?"
"Exactly."
Sai sank away in thought again. "Naruto-kun seems to think being considered a man is very important, or else he would not be so angry whenever I mention his almost non-existent dick."
"Let's not bring Naruto into this conversation. It's already awkward enough as it is."
"My apologies captain Yamato."
"Have you ever tried to get hard yourself?"
"Is that possible? The books I had to read for Root never mentioned that..."
"Yeah, you just, you know, play with your dick. Rub it, stroke it, jerk off, that sort of thing."
"I see… I will try that. Thank you captain Yamato."
"Don't mention it Sai," Yamato said with a smile. "I'm already glad that I could help you."
Sai smiled an almost sincere smile, before standing up and sitting down again on the edge of the pool. Yamato gave a puzzled look, until he realised what was going on. "Ah! Sai, you should really do that in private!"
Sai looked at Yamato. "If I do it here and now, you can tell me if I am doing it correctly."
Yamato stared at the boy. There was no denying his logic, but still... He couldn't just teach one of his subordinates how to masturbate, could he? Couldn't he? It wasn't like it was illegal, they were both of age. There was no harm in this, really.
Yamato sighed. "Alright, do it."

Sai started tugging his dick with little finesse, using far too much force to make it feel good. For a few minutes, Yamato looked at the display with pity. Then he couldn't take it any more and stopped Sai. "Okay, this ain't working. Just stop."
"Am I doing something wrong?"
"No, you're doing everything wrong. Your dick isn't an enemy you have to defeat and jerking off isn't a mission you have to clear. It's supposed to be fun!"
"I am not really that well-versed in having fun."
"So I noticed..."
Yamato stood up and sat down next to Sai. "Look, you have to use less force. Go easy on it." He took his own hard-on and slowly started stroking it. "See? Like this."
Sai look attentively for a while and then brought his hand back to his still flaccid penis and started mimicking Yamato's movements.
"Doesn't that feel much better Sai?"
Sai nodded. "It does, thank you captain Yamato. I think it is working."
As expected, Sai's penis slowly started growing in his hand. A sight that had an oddly arousing effect on Yamato. An effect he did not altogether mind. "How does it feel?"
"V-very good," Sai stuttered. He was trembling softly, overwhelmed by the new sensations he was experiencing.
"Now wrap your hand around your dick and move it up and down. Like this." Yamato started masturbating in earnest, Sai soon following his example. Before long, Yamato started to speed up, his eyes taking in every inch of Sai's slightly trembling body, his ears catching all of Sai soft moans and whimpers.
Far sooner than he was used to, Yamato's orgasm drew near. For a moment, he tried to postpone the inevitable, but then Sai climaxed. "C-captain Yamato! I...! I...!" Sai moaned loudly as his orgasm overtook his body. The mere sight of the young, supposedly emotionless, boy's first orgasm was more than enough to send Yamato over the edge as well. He climaxed calling Sai name loudly.

For a while, they lay side by side, both panting from the exertion. Then Yamato sat up and looked at Sai, who was all but completely exhausted. He smiled and started cleaning them both up. "I think it's time to go to bed, wouldn't you agree?"
Sai just nodded and made a weak attempt to stop Yamato from cleaning him and doing it himself. An attempt that was easily stopped by Yamato. "I think you spent enough energy today."
He picked Sai up and took him back inside the house. As he helped Sai into his sleeping bag, the boy suddenly stroked Yamato's cheek and smiled sincerely. "Thank you captain Yamato."
"It was my pleasure Sai," he answered as he returned the smile. He tried to think of something more to say, but Sai had already fallen asleep. "Ah well, I'm sure there'll be a next time."
A lustful grin grew on his face and he entered his own sleeping bag. "I guess this mission wasn't so bad after all."