After entering his upgrade period, Hachiman decided to "sleep" for the first 200 or so years, 'Sitting in a room by yourself is really devastating to the spirit, how do fictional characters make it sound so easy?'
The hardest part of the Ryumyaku and senjutsu chakra assimilation progress was going to be these first 200 years, he wouldn't gain anything from staying awake anyway, so he just controlled his body to do certain things on autopilot.
Now, for the last 800 years?
Well, the room he was in wasn't just empty, it was an underground chamber protected by countless seals containing many different targets he could keep replacing with Wood or Earth Release.
Having assimilated the most dangerous first batch of the Ryumyaku chakra that had been processed into senjutsu chakra, Hachi was feeling pretty great, he had reached the fifth step to Godhood he had set for himself.
This meant he had reached: the third step, an extremely chakra dense body with almost instantaneous regeneration from regular non-fatal injuries; the fourth step, a body that can absorb and use natural energy as naturally as breathing, elevating chakra and body quality to another level, increasing the user's regular perception to the physical limit; the fifth step, having the entire body's chakra be permanently merged with natural energy, achieving perpetual Sage Mode as a natural body state, becoming one with nature and obtaining almost inexhaustible energy, any injury that does not cause instant death can be recovered from as long as there's natural energy available for absorption.
'I'm probably comparable to an existence like the White Snake Sage that becomes one with nature, being able to mask one's presence from most and sense almost all things within one's perception range, but more importantly, having inexhaustible vitality and healing with the help of natural energy.' Hachi assessed himself with a silly smile plastered on his face, much like a mental patient imprisoned in this isolated room.
'Next is trying to achieve the sixth step, creating a body similar to Edo Tensei, but superior, a living body with perfect self-sustainability, never losing power, allowing for extremely rapid chakra recovery and a healing factor that would force an enemy to give up on killing me unless they can instantly pulverize me with something like the All-Killling Ash Bones... the more I think about it, the more I realize Kaguya-chan is no joke, how did Kishimoto think it was reasonable for her to lose to two kids with the handed down powers of only one of her sons?' Having seen Kaguya's power with his own eyes, he knew that no matter how inexperienced you tried to say she was, her powers are just too terrifying for two kids at the level of Naruto and Sasuke to deal with.
'As for the seventh step, I really don't know if it's possible, but since the Tailed Beasts can become immortal by having their will be part of their chakra, can't I try to merge my own will into my chakra so that it can automatically reform a chakra body similar to Bijuu for me even if I die? As long as there's some lingering chakra I've once used still around, that is, wait, because all my chakra is now senjutsu chakra there's a chance I don't even need my past chakra to revive, maybe natural energy will automatically gather with any surrounding chakra and pull in my remaining will.'
'This step will also make my chakra reserves truly monstrous as there would be no limit to their growth, as long as I can keep finding dense chakra sources like the chakra fruits or the Ryumyaku, I can integrate them into me instantly with my will. At some point I'd have so much chakra that even if I tried my best, I might not be able to run out of chakra, and if I somehow did, it would just recover at an extremely unreasonable speed with my Edo Tensei like body that doesn't tire but still has vitality.' It sounds so unfair to his enemies, but that's what makes it so exciting, Hachiman calculated that, unlike this seventh step, the eighth step will enable him to pulverize the entire Earth in a single move.
For a moment, Hachiman was a bit scared of growing too strong and just wiping out the entire Otsutsuki clan with a senjutsu chakra fart, but then he remembered there was once a monster like Otsutsuki Shibai and that the Otsutsuki are probably not the only powerful force in this universe.
So while pretty much none of the enemies seen in the Naruto series would be able to beat him when he was done upgrading, the enemies shown in the series are just a fraction of what this universe has to show, and there should also be higher level planes of existence since that guy Shibai exists.
'Fuck my life! I would never be this fucking scared if it wasn't for such an unreasonably fucking strong bastard that's fucking clairvoyant and almost fucking omnipotent! How does eating a fucking basket of fruits get you to literally ascend? Is that normal? Is that even fair?' Hachiman said calmly.
For the next 600 or so years, Hachiman devoted himself to achieving the seventh step–he succeeded.
It wouldn't have taken nearly as long to reach the seventh step in other circumstances, but to absorb the entire Ryumyaku, especially with natural energy to boot, and then instilling his will into every piece of that vast senjutsu chakra sea is simply not something that can be done in an instant, it's like instead of becoming the Ten-Tails jinchuriki, you try to devour the entire Ten-Tails and assimilate it's power directly into your human body, one takes mere moments, while the other takes a ridiculous amount of time for a regular human–on the other hand, now that his body had finally reached the seventh step with thr Ryumyaku fully absorbed, if he found another primordial chakra vein or chakra fruit, he could almost instantly absorb it.
With the upgrade being finished, Hachiman no longer needed to be attached to the God Tree sapling, he could move around however he wanted to, and if he felt like it, he could just go out and instantly dominate the entire Shinobi world.
But considering he didn't know which enemies could be watching, such as the wildcard that is Jashin or someone with the level of clairvoyance of Shibai, he decided to first refine his newfound power and work on all the ideas he had come up with, especially trying to make his own unique set of Kekkei Mora, as it seemed that by obtaining a great amount of chakra like with a chakra fruit, the Otsutsuki could awaken especially unique and powerful abilities, so he decided to take this chance where he couldn't kill himself even if he went crazy with body modification to tinker with possibilities.
'I've got nearly 200 years until Hashirama and Madara found Konoha, and I can sense two chakra signatures similar to Hagoromo's in the living world, so my incestuous gay grandkids must've gone through a similar situation this time.' Satisfied with his new long-range sensing capabilities, he overlooked the absolutely terrified faces of the nearby Tartarus Research Shinobi when he suddenly let his chakra burst forth, some people dissatisfied with bearing a curse mark for an unknown leader immediately realized that maybe it wasn't so bad.
Hachiman was still thinking of how to find a place to train high level techniques without destroying the world, Hachi realized he'd definitely need an improved space-time technique, but that would take some time to develop even with the explanations Kaguya had given him.
He also needed to do something about the Kara dimension, at the very least, he knew it stored Otsutsuki Shibai's body and the juvenile Ten-Tails Isshiki cultivated in Boruto, but since Kaguya one shot the weakened Isshiki, this dimension and any others that may be out there were another reason to improve his space-time capabilities, his hope was to develop an improved version of Kamui that was worthy of being named Divine Power.
'I'm thinking about too many things, there's no urgency, I haven't even pulled out my life support yet, let's get out of here first.' Hachiman wanted to go sightseeing around Tsukigakure, since he isn't a pervy old man that watches his village through a crystal ball–he would only do it through a 4K monitor.
Before leaving, Hachiman replaced himself as the Land of the Moon's generator, connecting the God Tree to the previously prepared chakra source in the chamber below his, it was Godrick, a massive Jörmungandr inspired serpentine monster grafted from some of the beasts captured by the Seals in their explorations, even though it's insides were a monstrosity, Hachiman made some clothing for it that made it look like a big snake instead of several beasts grafted together.
His underground chamber had no doors, so he teleported to a Raijin mark he had left in one of the eight Council member's badges, once there, he found himself being held like a princess in the arms of a pretty lady with a comforting embrace, even though his senses were superhuman, it seemed that he simply couldn't stop this from happening.
Minamoto-Mori Fumi was the youngest acting Council member, she had long brown hair, olive-tanned skin, and a pair or black eyes with a red tinge.
Fumi had just come home from a council meeting, when she was about to find something to eat in the kitchen, a man wearing nothing but baggy harem pants suddenly appeared directly in her arms.
She was quite tired today, so she held him in her arms for about a second before completely freaking out and aiming her hand at the man's throat; but before she could strike, the man teleported again, now standing right in front of her with an innocent, amiable and awkward smile.
"Good reaction, young Council lady, I'm sorry for intruding into your home so abruptly, it was just a random teleportation, but as a council member, you must have heard about the village founder and the only Tsukikage, right? I have never seen you before, so you must be new." said the seemingly jovial man with an appearance similar to Jiraiya's disciple Yahiko, having a pair of sharp cinder eyes that seemed to burn like magma, white skin with Sage markings that looked like black tattoos in the patterns of the lines that adorned the Tron suits all over his body, and of those lines, only two were on his face, they went from the far side of each of his eyes to his jaws like tear streaks, he also had eight black magatama forming a sun-like circle on his upper back, all of that was paired with an athletic, toned body akin to a Greek God–this man also did not teleport randomly at all.
Fumi immediately used her comms badge to ask an older Council member about the Tsukikage's appearance, getting a description that matched, and realizing that the man in front of her did just teleport twice, she relaxed, and while now conflicted on whether she should feel wronged for never have been shown their leader's appearance, she said, "It seems you really are the Tsukikage-sama, I'm Mori Fumi, I have indeed just joined the Council, so I'm sorry for not recognizing you, Tsukikage-Sama. I have to ask, though, I heard you were forced to remain in a restricted underground chamber to survive aging, so why have you suddenly come out completely fine?"
Since everyone in the Council knew about their leader's situation, she was naturally curious about the reason he could suddenly come out, and while she didn't say it, she really wanted to ask why this supposedly legendary suddenly showed up in her house without a single warning when she was about to have a good meal and relax.
"Nice to meet you, Fumi-chan, to answer your question, well, I guess my treatment is over, so I wanted go on a tour around the island, I just teleported to one of the Council member badges you guys have to catch up." Finally moving around unrestricted and having been embraced by a beautiful woman after so long, Hachiman was feeling great.
While in the past he wouldn't be this unserious with anyone besides Kaguya, staying cooped up for so long had left him a little lonely and now his personality had turned a little more... eccentric.
Fumi naturally noticed this fact, she knew that the leader's teleportation could not have been an accident, and considering he was only wearing some loose baggy pants, she almost thought he was a pervert, but Fumi already knew about his unpredictable nature and long solitude from her fellow councilors, so she didn't judge him too much for acting a little weird after getting freed.
"I understand, Tsukikage-sama, but do you want to maybe go to the Moon Palace and get some clothes first before going around the village?" Even though she was relatively easy-going, Fumi really didn't want to walk around town with a shirtless man wearing baggy pants, it's not like regular people even know that there's a Tsuchikage, most don't get into contact with high-level matters or reasearch of the village, so they don't believe the "myth" of the founder being alive, they at most just think that the island is the final resting place of the Moon Goddess' emissary that founded Tsukigakure, not the home to his intensive care unit.
In short, she wanted him to at least wear regular clothes, it would be even better if he wore that cool silver cape and hat Tsukikage set she saw hanging in the wall of Moon Council meeting room–Fumi thinks this eternally youthful old man would look quite handsome and respectable in a robe like that.
When Hachiman heard that, he felt quite embarrassed by his lackluster return outfit, he didn't even change his clothes before going out, 'I mean, just look at Naruto, he looked his best when he finally came back from training Sage Mode, the same goes Sasuke after leaving Orochimaru, how could someone of my current standing let teenage lovers have more grandeur than me?'
Hachiman decided to use Yin-Yang release to make himself a high-collar Six Paths robe similar to the ones his sons and the people that subsequently got their powers wore, it specifically looked similar to Indra's, the main difference was that it had fire patterns similar to Minato's cape at the bottom, a large crescent moon symbol, just like the ones Tsukigakure shinobi sported in their forehead protectors, was placed on the back and one on each sleeve; lastly, there were eight magatama in the front instead of the usual six, the reason is obviously because his name is Hachi'man, not Rokuman, 'And to go even further with the fitting name trope, maybe I should also carry eight flags on my back.'
In the end, he decided against the idea, eight flags were just too cumbersome even if he made them float, he also thought about whether to make himself a truth-seeking staff, after all, he had obviously learned how to make those.
Since he didn't want to damage his village's flooring, he decided to just make a wooden staff with his Wood Release, the temptation of looking like a Sage was simply too strong–as for necklaces and other accessories, he simply didn't want any.
Fumi watched Hachiman nod to her suggestion, pulverize his pants, stay butt naked for a couple of seconds, and then, with a look of realization, materialize a Sage robe and staff from thin air, 'So the tattoo lines don't reach down there... wait! Why did he think it was okay to get naked in front of me? Were people of the past so liberal?'
Seeing how the Tsukikage in front of her didn't say anything, Fumi forced herself to suppress the doubts in her heart and asked, "Should we go out for a meal then, Tsukikage-sama? There's a great barbecue restaurant down the road from here."
Hachiman actually didn't notice his accidental flashing even after doing it, so, with not an ounce of shame and remembering Nobu's barbecue, he responded enthusiastically, "Barbecue? That's my favorite! Let's go!"