Today had been a good day for Senju Nawaki.
When he came back from the Academy, he found out his beloved sister and his brother-in-law had come back from their trip.
Needless to say, the little one was ecstatic.
"Nee-san, you're finally back!" Unfortunately, another person was also back.
Nawaki didn't have a good impression of his brother-in-law—"Why?" You may ask?
Because Ieyasu constantly berated him verbally, whenever he said he would be Hokage, he'd make fun of him saying the future Hokage can be killed by the Kurama's fart—he never even told him who Kurama was.
Ieyasu didn't want to get involved with Kurama until it was transferred to Kushina, only with her would he have a chance to make Kurama reconcile with humans—Mito already treated it like a monster that couldn't be trusted with freedom.
On a different note, Nawaki also greeted the unpleasant man his sister liked, "Hi there, Ieyasu-niisan."
"Oh, come on, you can just call me Yasu-nii, boss. Anyways, wanna spar?"
'This again, why does he call me boss? And no, I don't want you to beat me up while saying I'm not even good enough to be bait.'
This Nawaki had come to understand people could be extremely odd. "We trained a lot in the Academy, so maybe we can spar next time."
Ieyasu immediately grabbed Nawaki by the collar and teleported to the Forest of Death. "Come on, boss, where's your youth?"
"What do you mean youth? Why are we here? Wait!" As Nawaki feared, Ieyasu decided to kick him down the tree and teleport back home. A future Hokage had to train, not scream and shout and then kill himself because he was too "pumped'.
'Can't let this brat be weak and clueless like that at twelve, he's Senju Hashirama's grandson, after all. So you're not making Tsunade sad on my watch, kid. Besides, it's good that I can get more alone time with Tsuna.'
So he did just that, he immediately appeared back home and was all lovey-dovey while Boss Nawaki suffered in the Forest of Death.
Training ground 44 had its reputation for a reason, it was truly troublesome even for Shinobi, the sheer density of hazards and the unfriendly environment could threaten and exhaust anyone.
It took Nawaki nearly three hours to finally get back home.
When he arrived, the demon that claimed to be teaching him offered him some fruit juice and smiled as if he was kind, "Welcome back, Boss! Let's see how long it takes for you to make it back tomorrow, and oh, there's no need to thank me for my teachings, see ya!"
Nawaki felt deeply aggrieved with the situation—it was one thing to not be able to beat him, but he couldn't even verbally berate the culprit after he tried to make himself look good.
He thought to himself. 'Too shameful!' As he drank the cool fruit juice.
Nawaki immediately went to complain to the only person that could stop his brother-in-law.
"Nee-san! Can you tell Ieyasu-niisan to stop torturing me like this? I really can't take it!" He really looked like a pitiful boy.
Tsunade felt a little bad, but she also knew Nawaki was truly too weak to back up his recklessness, and she also felt like this was good for both of them to get close, so she pretended to not understand, "What torture? He's just teaching you like our teacher did, this is what you have to go through if you want to be Hokage! It's your choice."
"But..."
"Nee-san is feeling tired today, I'm going to rest now, okay? Wash up and eat before you go to bed, you have school tomorrow." Tsunade wasn't about to stubbornly refute reasonable complaints, so she wisely retreated.
"Doesn't she care about me at all? It must be that demon! Damn it! Even the Hokage is on his side, Dad, Mom and Grandma Mito wouldn't do anything either..." Nawaki gave up—he had reached the threshold of despair.
He resigned himself to his fate for now, at least there would actually be improvements to his skill, "I'll just eat so i have energy for tomorrow."
...
The next day.
Nawaki went to the Academy like any other day.
It was a pretty ordinary day until he left—as soon as he stepped foot inside his home, he found himself atop a tree. "Why?!"
As he yelled in grievance, Nawaki already found himself being sent flying by a sole kick.
"Ah, hitting kids really is cathartic, why is Orochimaru so nice to them? I guess that's the difference between the great and the mediocre." Ieyasu felt proud over his abuse of children, distinguishing himself from the well-known serpetine pedophile.
He was waiting to fully integrate the Ryumyaku, so he didn't have much to do these days—what better past time than training the next generation?
With that thought in mind, he almost became a Jonin instructor or Academy teacher, but he thought it was too troublesome.
And with war on the horizon, he'd put any real teaching thoughts on hold.
After all, if he truly became someone's teacher, he'd never accept doing a half-assed job.
...
6 months later, Nawaki could finally dodge a kick.
"Incredible! This is it, you've graduated from the Forest of Death, Boss!" Ieyasu was actually a bit surprised, it seemed like he really had a knack for teaching.
"Wait, really? Is this another unfunny joke?" Nawaki wasn't really happy, he had gone numb.
"What? Of course it's true! I'd never joke about this type of stuff... twice."
"Okay, then please get me out of he-- Why do I even try?" Nawaki familiarly navigated the terrain, wondering why he never learned. 'Of course he'd leave me here!'
Ieyasu didn't actually plan to leave him there, it's just that almost as if by a coincidence of fate, he had just finished absorbing the Ryumyaku—maybe that's why his kick was off?
'Well, I'll cut him some slack, I can't take away Boss's graduation like that.'
'Hm, it seems like I'm literally built differently now. I'm no longer a regular human. It feels like I have a greater affinity to all things, energy, chakra, souls and space-time. It's a very slight difference, but it means I can reach greater heights with a lot more ease in the future.'
As he thought of teleporting without a predetermined Flying Raijin mark, Ieyasu found out he could do it!
'I can actually form a temporary seal for teleportation as long as it's not too far from me. Hm, it's going to take a couple weeks to get it down, but then I'll be able to instantly teleport in my vicinity. I could probably do it up to a 100-meter radius for now. This means I can also sense all changes in space-time within that distance. I also feel like the Byaku-Sharingan can also detect space-time phenomena and other dimensions now.'
'Wasn't it not supposed to evolve? Why did it first develop soul vision and now this? Is it because it's an improvement that comes from myself and not the eye? That makes sense, even a regular Shinobi can enhance their senses, why couldn't I with my Adaptive Body cheat do it? Anything is reasonable! Truly a top-tier bargain, five-stars is simply not enough to describe my satisfaction.'
After he teleported home, Ieyasu remembered he was supposed to give Tsunade a sort of "Ryumyaku seed" or mini-source to her, so he went and found her.
"Ouch!" Ieyasu got elbowed in the chest as soon as he teleported behind Tsunade.
"Do you really like getting hurt? I've already told you, I can't stop myself from instinctively hitting you if you show up behind me. It's even worse as my brain doesn't register you as a person I shouldn't him." Tsunade was brutally honest, she also knew that although he didn't quite enjoy being hit, he didn't mind it either—she would do it slightly less often if that was the case.
"That hurts my feelings, how can you not care for your own husband? And here I was, bringing good news to such a wife."
"Spill it."
"..." Ieyasu wondered if he should act pitiful.
"Just do it already or you'll ruin my mood."
"Alright, alright. The news is that I've finally assimilated the Ryumyaku thing I got back in Roran, I was here to give you my seed."
Tsunade immediately hit him with a left knee to the liver for spewing out such a stupid innuendo. "Stupid."
"Can't you play along for once? That hurt, damn. Anyways, focus on absorbing this, it should be easy for you, but you should still be careful."
"Okay." Tsunade also got serious, she didn't want to waste a gift or have any accidents happen.
Ieyasu immediately placed his hand on Tsunade's chest.
"Seriously?" She didn't mind, but he just asked her to be serious and then proceeded to grab her chest—it didn't exactly evoke professionalism.
"I just thought it was a comfortable position, I can do it from the back if you prefer it too."
Tsunade didn't even bother to hit him again for the stupid innuendo—it was a good one this time.
"Go ahead."
Then, Ieyasu places his hand on her back and essentially started cresting a Tsunade-shaped Rasengan inside of Tsunade's body.
You can imagine how painful this would be, but both of them were monsters that didn't even process pain the same anymore—Tsunade actually controlled her pain receptors with her chakra control and medical experitse, but Ieyasu was just a freak.
Anyways, the whole point of this was to create a "chakra storm" that Tsunade could quickly absorb and integrate into her body through her speedy healing.
This couldn't really be done by anyone else, except for maybe Hashirama, but he didn't need it in the first place.
"I'll stop whenever you tell me or when I feel like your chakra has reached the self-sustaining threshold that sparks virtually limitless recovery." The process was basically like nuclear fusion—with enough stuff in a certain space, it suddenly did some crazy shit.
This was what Ieyasu discovered, just like matter, chakra also had a special phenomenon caused by density, this is what he called the Threshold of Perpetuity.
Chakra entered a state in which it became virtually endless.
In practice, it was obviously not, but the recovery rate became absolutely ridiculous, and the recipient would always have a minimum amount of chakra—all that meant one thing, chakra exhaustion became impossible.
So in practice it really was almost like endless chakra as long as you weren't planning to spam Moon-destroying moves one after another.
After what felt like an hour, Ieyasu felt the difference in Tsunade's chakra, at that moment, both of them thought the same thing, 'It worked!'
Ieyasu felt conflicted, though, so he just asked, "Should I stop?"
Tsunade didn't completely understand, "What do you mean? If you can keep going, couldn't we just keep infusing chakra into each other and have infinite chakra?"
"Hm?!" Ieyasu felt like his mind got struck by a lightning Boruto, but then he remembered something. "Oh, we actually can't, but I can probably give you at least double this chakra by the looks of it."
"What looks? Oh, your eyes. What stops us from doing that, though? What sets the limit?" As a medical-nin, Tsunade was obviously quite curious.
"Surprisingly, it's our soul. Our own inputs simply can't increase our chakra beyond the certain limit that our soul can hold. That limit can only increase with time, unless we use a ridiculously high external chakra input like another Ryumyaku."
"Well, technically my soul could adapt to more input, but you can't produce enough output to force it to that extent, I'd also need to simply wait or use another high-density source of chakra to increase my reserves further."
"Well, then just go to the limit, we can worry about other things later. This is already a ridiculous amount of chakra that I can't even spend. It will also already take a couple of weeks before I can control the new chakra as well as I do normally." Tsunade felt very blessed to have such an anomaly as her husband, she'd never even have this knowledge or opportunities to increase her strength without him.
...
It took Ieyasu three more hours to completely fill her up from the back.
The resistance, or "chakra drag" as Ieyasu called it, increased with density, so it took roughly three times longer to reach the plateau even if it wasn't three times as much chakra.
At this point, both of them weren't actually exhausted, they were simply monsters in all aspects, so this whole process was only a bit taxing on their focus.
"Thanks, Yacchan. I guess I should return the gift properly this time, take us to the Forest of Death."
Then, Ieyasu spent a few more hours filling Tsunade up—if they didn't have some sense, they could have gone on endlessly.
After the whole deed, Ieyasu looked at the devastation around them. A large section of the forest had been replaced by thick groves of unnatural trees.
"Thankfully Nawaki won't come here anymore. He might notice I subconsciously replaced an acre of terrain with Wood Release."
Then he folded his arms and solemnly nodded to the sky.
'Thank you for helping me survive, Shodaime-sama. I couldn't have endured your granddaughter so smoothly without your divine cellular assistance. You have my eternal gratitude. I vow to deal with your wife—ahem, your brother Madara—properly.