Eden had been a fool, and a victim of his own bias.
All this time he had tried to use life and death crisis to learn Reverse Cursed Technique, because it was how others had done it.
And yet, after all of this, it was a beautiful sight that had done it.
The shame burned hot, and Eden understood it all came from a simple misunderstanding. His belief that the learning, or maybe awakening would be a better term, of Reversed Cursed Energy came from Cursed Energy.
It was most often referred to as Reverse Cursed Technique, but in reality a Reversed Cursed Technique was activated through reversing Cursed Energy, turning it positive, and running it through one's Innate Technique, thus activating it in reverse.
As for the healing part, it was just the influence of Reversed Cursed Energy.
Since Reverse Cursed Technique came from Reversed Cursed Energy, he thought everyone shared the same way of awakening it. After all, techniques were unique to people, or bloodlines at least, but Cursed Energy, everyone had the same.
And since everything was born from Cursed Energy, Eden thought everyone would awaken Reversed Cursed Energy the same way.
But that was where he had been mistaken. It was not that different people awakened Reversed Cursed Energy differently, it was that the process was done through one's technique instead.
One needed to deeply understand their Innate Technique, and from that understanding they would learn to reverse their Cursed Energy through their technique.
Eden did not know how exactly Gojo Satoru had come to a deeper understanding of his Innate Technique through nearly dying, but it did not matter.
Even though a part of him felt bitter that something that had eluded him for five hundred years had been so simple and right in front of him, the joy from learning Reverse Cursed Technique and how to make Reversed Cursed Energy overpowered that.
Playing with the flame, which he noted was not cast with the Angelic Flame, Eden felt his connection to his Cursed Energy had deepened, even more than a Black Flash could have. Observing this new facet of Cursed Energy, this reversed version, brought his vision of it to the next level.
Extinguishing the flame, Eden curiously looked at his skills.
[Dismantle (7th Rank): Launch an invisible slash with a range of 50 meters to deal 500 magical slashing damage. Output: 1370 CE.]
[Cleave (7th Rank): Inspect the target and use the exact amount of Cursed Energy required to cut them apart. Must be in contact with the target, deals a max of 685 magical slashing damage. Output: 1370 CE.]
[Domain Expansion: Malevolent Shrine (8th Rank): Form a domain with a radius of 150 meters around the activation point, lasting for two minutes. While active, everything other than the user is relentlessly attacked by Cleaves and Dismantles two ranks below Maximum Output, stops any form of teleporting out, while the user is boosted by 50% in all manners, MP regeneration becomes ten times faster and Divine Flame can be freely used.]
[Divine Flame (8th Rank): Form a flame that ignores Fire Resistance III and Fire Immunity III, dealing 870 fire damage. Can only be used on targets on whom Dismantle and Cleave have been used.]
Eden's Maximum Output was getting very close to his upper limit, which was something he figured only someone like Gojo with his Six Eyes could manage. Actually, Eden would bet that aside from someone with the Six Eyes, no one else could boast a better Cursed Energy Manipulation than him.
And the skills themselves, they were absurdly powerful. Just his Dismantle had passed the threshold of Tier III damage. His Cleave was well over it now, at 685. Were he to face Tiamat again, he might actually be able to cut off one of her heads in only two or three Cleaves.
His Domain Expansion also received two boosts: one was a visible one, as its duration had doubled, and an invisible one, as now that he had mastered Reversed Cursed Energy, Eden could heal his brain and the Innate Technique engraved on it, and thus cast his domain several times a day like Gojo and Sukuna had done in their fights.
As for the brain damage, Eden did not care, his physiology could heal all physical damage and put him back in his prime state.
Of course, that was a skill he would have to learn, but since the two had pretty much come up with it on the spot, or at best used a few decades to learn it, he did not feel like it was so far out of reach.
Lastly, his Divine Flame. It was an 8th Rank attack, and Eden suspected that all of his techniques were at their peaks. The reason for that was that he could feel himself standing before an imaginary wall, and felt that any more progress with his output would be near impossible. He had hit some kind of hard limit for a Tier I, or someone without something like the Six Eyes.
For that limit to be at the upper limit of a rank only made sense, and Divine Flame appeared to be firmly one rank above Dismantle and Cleave. Any more progress might thus push Divine Flame into 9th Rank, or Tier IV, which was why he believed the hard limit was there.
He was already using spells and techniques two Tiers above his own, three would be unthinkable. He was pretty sure that two already was for basically everyone else. Eden did have some unique circumstances after all.
Back to Divine Flame, not only did it deal a lot of damage, but it could also straight up ignore Resistance and Immunity. It was at Tier III at the moment, but he imagined it would grow along with the skill.
The only visible drawback to it was that he needed to use Dismantle and Cleave before that. Eden knew that there was one more though, both from his memories of the manga and his own knowledge of the technique, and it was that Divine Flame had a small range and slow speed.
It might sound cryptic, but it was because of the system's description of it, which only displayed damage and range, not how things worked.
In reality, nothing stopped Eden from manifesting his Divine Flame whenever he wanted. He had just done it, despite not using either Dismantle or Cleave before.
But Divine Flame, by itself, actually did nothing, or it would be more accurate to say it dealt no damage. Eden could throw it onto a tree and it would harmlessly bounce against it.
That was because Divine Flame could only act on something when it had been Cleaved and Dismantled.
Eden did not know how his technique worked exactly on the molecular level, since he could not see at that level, but he understood his technique on a conceptual level, and he could extrapolate from that.
Whenever Eden used Cleave or Dismantle, he did not really conjure an invisible blade. It was not an invisible sword. Rather, he created a property through his Innate Technique, that to cut and divide, expanded it with Cursed Energy, and when that property clashed with something, the property would be applied to it.
Whether something would be cut would then be calculated by pitting something's toughness against the potency of that property, which itself would be calculated based on the output of Cursed Energy.
In Dreamland terms, that cutting property would be translated into a Magical Slashing attack value, and would clash against something's defence value, and like any other attack, depending on that result, the thing would be cut to a certain point.
Functionally, it worked the same as an invisible sword, but it was not one.
Divine Flame did the opposite of that. Like any Innate Technique, when activated, a property would be created. But instead of being cut and divide, this one is assemble. One might think this would give a healing property, but it did not heal, it assembled.
On molecules and atoms that were already whole, it did nothing, since there was nothing to assemble. But if these same atoms had been cut apart by another property, then Divine Flame had something to work with.
And whenever atoms were reassembled randomly, messing up with the balance between protons and neutrons, an extraordinary amount of energy would be produced.
Normally, this would simply result in an explosion of energy, but since it was born out of Cursed Energy, all that energy went into feeding the Divine Flame instead, turning it from a harmless flame to a fire with nuclear power. In a sense, it internalized and concentrated the energy into the form of the flame.
As exciting as that was though, it was not perfect. First, the assembling had to be guided by Cursed Energy, so there was no cheating around needing to use both Dismantle and Cleave. The two had to be used as well, since they did not exactly cut in the same way conceptually. Cutting someone with any other means would also be useless.
More importantly though was the usage of Divine Flame.
Although Divine Flame would not explode in his face, Eden himself possessed no Resistance or Immunity to Divine Flame. An easy solution to the flame's slow speed would be to coat it through his fists and punch people with it. But once the Divine Flame was 'ignited', it would still be on his fist, and burn him.
Whoever he hit would certainly be turned to cinders from even an instant touch, but so would his fists, and probably the rest of his body.
Resistance and Immunity was also useless for it, and even if he picked Fire Immunity for his next Divine Boon, it was only Fire Immunity II, so useless.
That meant Divine Flame had to be used at range if he wanted to live, but after some testing, he found its range to be of only ten meters. This was more than enough for Eden to be safe, since he only needed the Divine Flame to not be physically attached to him, but then came the speed of it.
It was about as fast as an arrow, which might seem fast, but Eden had reached a level where an ordinary shot by a mortal was next to impossible to hit his enemies. Well trained Tier 0 could dodge arrows, so hitting a Tier III with something going at that speed is wishful thinking if they are not immobilized.
This did bring Eden to a few ways of dealing with that problem. One was using magic that immobilized his targets, for example Time Stop. However, most, if not all, were debuffing magic, and with basically everyone having Magic Resistance at that level due to sheer attributes, it would take extremely high level magic to do that.
And by that point, he might as well just learn a high level offensive spell.
Even Time Stop did not stop the river of time. It only temporarily froze beings in time, so it was a debuff. That was why Eden had been immune to it when he met Mystra, and why he never bothered learning something that seemed so powerful.
It would have been a good solution to the Divine Flame problem, since targets would only get out of the Time Stop whenever the spell ran out or they were hit by an attack, and getting hit by Divine Flame was pretty much the end for anything, but anything that would warrant the use of it would be immune to Time Stop.
So, Eden went for the same solution as Sukuna: a Binding Vow.
[Play with Fire: Divine Flame no longer can be used outside of Domain Expansion, Sure-hit effect inside Domain Expansion erased. Malevolent Shrine's range is doubled, Divine Flame spreads to the entire domain when used, and cannot damage the user.]
Eden's Binding Vow shared things with Sukuna's, though they were not exactly the same, simply because of Eden's opinions.
The original Binding Vow of Sukuna sacrificed his ability to use his Divine Flame while outnumbered outside of his domain, and in exchange he would not only get the increased domain range and presumable immunity to the damage, but the Divine Flame would also turn into a real nuclear explosion.
That meant that it no longer just dealt the fire damage of the Divine Flame, but also the shockwave itself, along with the instant pressurization and depressurization of air that would just kill anything.
Eden wished he could get that, but he believed it to be deeply unfair, and far too powerful. Maybe Sukuna's lack of knowledge on nuclear power had allowed him to think this was fair, but Eden could not vow this.
Again, what mattered the most when taking Binding Vows was one's beliefs, not actual physics. So if Eden believed it to be too unfair, he could not take the Vow with himself. It was not something that could be controlled either.
So he altered it, to the point where he thought it would be fair. Which meant he had to sacrifice something equally valuable to him to attain this great power. That point was the complete and utter inability to use Divine Flame outside of his Domain, and the erasure of his Sure-Hit effect.
He thought this was a fair counterpart, since he expected to be facing many battles against single opponents in the future, battles that Divine Flame may have trivialized. There was also the removal of sure-hit inside the domain, which was not that big of a deal, but also helped. The countless Cleaves and Dismantles would still target everything inside, but the attacks Eden performed himself would no longer hit for sure.
Of course, Sukuna's Binding Vow also played a role. The mere knowledge of something as outrageous as the one he had passed helped make the one Eden had signed seem more fair. Maybe Sukuna's own Binding Vow had had more conditions and clauses the manga never explored.
In any case, there was no going back, the Binding Vow had been passed. Eden, of course, felt strongly tempted to use it, but he did not want to ruin the landscape. It was what had allowed him to awaken it in the first place after all, so he used his divination magic to get a general direction for Iggwilv's realm, and set off.