Written in fifteen minutes when my mind pulled a few threads.
Better Off Forgotten
Most of the time, Hazō experienced his new connection to Jiraiya more as a weight than a ladder: it was a set of responsibilities he'd willingly adopted for power and a chance to matter, and frankly speaking, it wasn't a gamble that had paid off yet. In the short term, he'd have been strictly better off somehow joining under Jiraiya's aegis without becoming part of his new clan, because he'd have been given a chance to fade into the background until the next time he had a chance to try and change the world.
This was not one of those times. Clanless missing nin generously adopted into a village didn't get to meet with its leader on short notice without a given reason and without overhearing ears. The Hokage might be staring at him with an expression of faint annoyance, as if wondering what unpleasantness the young man had dumped on his doorstep this time, but the three of them were in the room with him, and that was the important part.
"Hello, sir." Hazō bowed his head stiffly, and Jiraiya inclined it a little in turn, not rising from where he sat. "I didn't want to separate from Noburi and Keiko when they could be ambushed, but... This is about sealing." Jiraiya's eyes sharpened, and he leaned forward. "Can you keep them and anyone else from overhearing, without them having to leave the room?"
"I need to know what this is about first." Hazō hadn't seen Jiraiya look this intense in any situation not involving a killbox or Naruto. It made him feel a little better, at least. If he was reacting like this--
"Sir," Hazō said slowly, "what are the basic Jutsu that every single ninja learns?"
Jiraiya grabbed him, pulled forward, and slapped down a seal. The world became suddenly, eerily silent. Hazō glanced backward, only to see that the two behind him couldn't be seen, shrouded as if behind a thick mist.
"A surprisingly circumspect way of putting it," Jiraiya said, as he faced forward again. "I appreciate that. Now, elaborate."
"I don't have my disguise kit--or, I should say, I don't have a disguise kit," Hazō said. "Neither do Noburi and Keiko. Following my incapacitation in the middle of the last event, I replaced my disguise and returned to the party. At no point afterward did I offload items from my storage seals in such quantities that could have lead to the complete loss of my disguise-related supplies, and we've been sleeping in shifts continuously since the last time I woke up, so I strongly doubt they've been stolen. That was what made me notice first. After that, I was able to look back over what I could remember of the past, and--" Hazō stopped, thinking of the best way to phrase it. "I don't have enough muscle memory of disguise techniques, sir, and the Iron Nerve doesn't forget. Never. The things I've done in the course of my past actions aren't compatible with my available skills at present."
Jiraiya nodded, face expressionless. "Your theory, then?"
"There is some extremely basic disguise Jutsu of sufficient width, breadth, simplicity and efficiency that the majority of genin don't need to learn more than the basics of alternative techniques." Hazō took a deep breath. "And this technique no longer exists, sir, as of some time between now and the end of that event. I suspect this loss is related to sealing."
Jiraiya was silent for a time. Then his mouth quirked upward, just a little. "Well, that's almost a relief. Of the Elemental Nations, Mist knows and no one else. I'll have to negotiate with that in mind. If I spin this right, we might not have a world war within the next five years."
"Sir, I wouldn't--!"
Jiraiya gestured once, sharply and dismissively, and Hazō fell silent. "Your bloodline's Iron Nerve possesses perfect physical muscle memory, which leads to a higher number of infiltrators and sealmasters among the Kurosawa clan. This missing technique relates to all three aspects, and therefore only its members are likely to realize the gap. The majority of top-class ninja possess the width and breadth of skills for their memories to rationalize away the loss, and the majority of lower-skill ninja lack the field experience to realize a strong discrepancy. I would suspect that perhaps one or two other Kurosawa have realized; unfortunately, your aunt is not quite Kage-level, and in her relative mediocrity, she is more likely to notice the lack. I suspected she already knows, but I'm glad to have it confirmed."
Hazō couldn't help picking the thread. He opened his mouth, but Jiraiya rolled his eyes and preempted him.
"Of course I realized, kid--I'm the greatest spymaster in the world, in more ways than one. If you have enough balls in the air then you notice when one gets jogged before it falls back in hand. Thankfully, I cultivate diverse skills in my field agents; consequences should be minimal, all the more when other nations should suffer more for the lack than Leaf. Unfortunately, your Aunt will realize as much, and due to her clan's experience with Sealing, she's more likely to notice the signs of a seal failure's intrusion upon reality. If I benefit, and being that I'm almost one of the greatest sealmasters in the world, I'm the most likely culprit. If I can weaponize sealing failures on this scale, then I'm a threat she can't let stand. Shame she's not good enough to get the attention of the Watchers--and I doubt any Kurosawa who would would talk about it without reason."
Jiraiya stared at him, and Hazō could see the gears within gears spin.
"Of all of Leaf, I suspect you and I alone remember; of all of Mist, perhaps a couple of Kurosawa do. I can use that; I just need to think about how. In the meanwhile, guard that secret like you'd guard the life of everyone you'd ever loved." Jiraiya rubbed at his chin, eyes set on some distant thought even as he continued to speak. "And before we go, a warning. You may eventually remember the specifics of that technique, now that you remember it existed. Do not ever attempt to use it. In the best case scenario, the Watchers removed it from our memories, and they will make an example of you some time after you use it--and an example of me, for failing to control you. In the worst case scenario, someone else fucked up, and there's a hole where that technique once existed; try it now and you'll pull the hole out into the world around you the moment you finish the final seal. Get lucky doing that and you just die. You don't want to know what happens to the unlucky ones. If you think you might, try talking to that uncle of yours about dimensional sealing failures again."
Something about Jiraiya's utter dispassion chilled Hazō's spine, and he ducked his head. "Yes, sir."
"More than that, I would suspect some missing-nin possess the ability, the unconventional skills, and the depth of experience to realize this. There is a non-zero chance that particularly advanced missing-nin may retain the technique. I doubt you'll face off against Akatsuki, or that you'd be able to do anything against them if you did, but you've surprised me before. Keep it in mind."
"Yes, sir."
"Good." Jiraiya clapped his hands, and the seal fell apart. He looked at each of the others in turn, and back to Hazō. "We're done speaking of this for now, but I may call you for matters related to it in the near future, Hazō. Remember what we talked about."
"Yes, sir."
"Then go."
"Sir."