Once upon a time a god created a universe, as gods are wont to do. Gods are powerful beings but when faced with a problem they will never ask for help. They will either try to solve it on their own or visit the universe of another god to observe their world for inspiration. Likewise a god will never directly offer help to another god as that would be an insult. Instead, should they discover that the visitor had a dilemma, they might show the struggling god how they themselves would or maybe even had solved a similar problem.
But even this indirect help is inaccessible to gods who don’t leave their own universe to seek it. Which this particular god had refused to do. The god had visited the universes of other gods to gather inspiration before making their own, but hadn’t left their universe since its creation.
Something the god had learned about when they explored other universes was reincarnation. Not all gods had added reincarnation to their universe and it didn’t always function the same way. Sometimes the soul had its memories removed before being reincarnated but not always. Some gods had restricted reincarnation to their own universe, while others decided to swap souls between them. In some universes reincarnation was only for sapients, in others not. And sometimes one could only reincarnate into the same species, while in others what species you were reincarnated into was dictated by your actions in life.
This particular god hadn’t intended on having reincarnation in their world. But the barrier between the different universes were made to be penetrated. By gods, mainly, so they could visit each other, but also by powerful spells and incredible technology. Additionally the barrier between worlds would be thinner in certain mythical places and on certain time, dictated either by calendar or celestial movements.
And while the barrier was thin or had a hole in it opened by powerful individuals a soul meant for reincarnation could wander through, completely without meaning to or even realizing they had.
This rarely ever happened, but when it did one of three things would happen. Either the wandering soul would be found by the local god, in which case the god might return the soul to its original world for their own god to deal with. Or the god would use the soul for their own purpose, risking the wrath of the soul's original god, should the soul in question have been intended for a specific purpose already.
But should the local god not notice the wandering soul - or simply decide not to do anything -, the wandering soul would enter the first empty and suitable body it could find. This could be a stillborn baby who now wouldn't be stillborn. Or a grown adult who rose again after a fatal blow from an enemy.
Sometimes, as it had happened this particular time, the wandering soul would enter a body which had been made with an intent to host a soul, but where a soul hadn't yet been inserted. Such as certain types of golems and androids.
In this particular case, the world's Dungeon Cores had originally been created to match and challenge the greedy and power-hungry sapients of the world.
And to do that, god wanted to make them sapients as well.
Only… None of the souls the god created and placed in a Dungeon Core could handle being a Dungeon Core. They all eventually went insane.
Some went insane with power and made impossible-to-survive Dungeons, which prompted the creation of certain laws of fairness all Dungeon Cores now had to follow.
Others went crazy due to loneliness as it had taken too long for them to be found or as their location was wiped from the mind of sapients, as the ones who had found the Dungeon were killed in battle between species. So god changed their relation to time and removed their ability to feel loneliness and boredom.
Certain Dungeon Cores would refuse to kill, which had them removing most of their creatures from their Dungeons to make them safer for visitors. Usually this happened as a result of having gotten attached to certain sapients who would still always die before the immortal Dungeon Core. Which in turn would lead to a massive depression, where the Dungeon Core simply stopped caring about anything, now having realized they would always outlive their loved ones.
But the point of a Dungeon Core was to kill and train. God couldn't have them be crushed by the reality of their Mission and so changed their innate understanding of death and stopped them from experiencing any emotion which could impede the success of their Mission. The god also ensured Dungeon Cores would have an innate desire for progress and a need to grow. They still wouldn’t be able to feel bored, but would instead feel restless, if no progress had happened.
Even this wasn't enough as the now uncaring Dungeon Core decided to forsake their Mission and focus only on the satisfaction of power, even limited by the laws of fairness.
Dejected, the god removed the souls from all the Dungeon Cores and made their decision making run on algorithms and randomness instead of conscious thought.
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It wasn't perfect, but it was better than before.
Then one day, a wandering soul entered a newly created Dungeon Core, becoming the first Dungeon Core with a reincarnated soul. The god saw that it was good and gave the new Core what blessings the weakened, resting god could.
Not even half a year had gone by before the god saw exactly how good this wandering soul actually was for their world. The soul, now Dungeon Core, had led the god’s most recent annoyance to ruin with both direct and indirect actions, making them worthy of an Achievement never before achieved.
And through the whole ordeal the Dungeon Core had never once strayed from their Mission.
With the exponentially dangerous attacks from the mind controlled followers of ‘The Order of The Broken Goddess’ many of the god’s original Dungeon Core souls would have sought mindless slaughter to be able to grow more quickly in order to defend themselves. But not this one. They seemingly hadn’t even considered it and had even let a target go back to the Surface World, hoping to aid the world outside their own Dungeon pocket dimension by releasing the infected individual.
An act aimed at fulfilling their Mission beyond what was asked of them and for no expected gain at all.
But a reward would still be given. Everytime a werewolf was to be killed for their lycanthrope nature, the Core would receive EXP as if the werewolf had died in their Dungeon.
Due to their slumber, the god hadn’t immediately realized that an evil mind controlling cult had begun to rise. The idea of Classes had been… inspired… by another god and the various mind control Classes had slipped in with the rest of them. The god the idea had come from had liked having conflict in their world and having underdog heroes come and save the day from seemingly impossible odds.
When the god finally took notice of the cult, it had grown too large for them to simply remove the Classes like they wanted to. Not only did a lot of people have the Classes, but the bigger problem was the much larger number of people mind controlled because of them.
Hoping to lower the number of affected people, the god gave every mind controlled member a Dungeon Weakness.
And now the reincarnated soul had - both directly and indirectly - been the one to cause the number of cultists to lower to such a degree that the god could finally remove those Classes for good. Their slumber had given them some energy back but with how low the number of affected people now were, it took much less to remove the Class from all who had been granted one and replace it with a new one.
But removing the Class from a sapient didn’t stop those already mind controlled from being so. It simply stopped the mind controller from using a System granted Skill to control the actions and mind of another. The cult was still there but would have a much harder time trying to expand. And eventually: It would cease to exist.’
A single reincarnated soul had done all that, before they had even been a Dungeon Core for half a year, where the souls of the first Dungeon Cores had all ultimately failed their Mission.
Clearly, this was the solution to the problem!
Newly created souls couldn't handle being a Dungeon Core, but apparently a reincarnated one could!
If that was indeed what had made this soul different from the others the god had tried.
It was worth a try at least. One last try to make Dungeon Cores actually efficient in following their divine Mission.
So, the resting god put a hold to their slumber and reached out to the original god of the soul now settled in a Dungeon Core. The two gods agreed to swap 36 souls to be reincarnated in the other's world as a test to see if reincarnation was something fitting for them and their worlds.
The god knew they wanted to place the 36 souls in Dungeon Cores, but that was more than ten times the number of Dungeon Cores created yearly. It would have unfortunate side-effects to change the number that drastically. And while they could take a decade to release the reincarnated Dungeon Cores in a more natural manner, the god was already longing for sleep and didn't want the hassle of having to keep the remaining souls from wandering and accidentally finding a suitable body on their own.
Instead the god made three new Dungeon Cores for the year all at once and placed a soul in each.
The remaining 33 souls were placed in the Cores of the world's 33 less efficient Dungeons. Dungeons where the algorithm or randomness of a non sapient Core had resulted in an undesirable outcome.
To gain as much information during the test, the souls would have varying amounts of memory from their previous life. Though, never enough for them to truly miss that life.
Additionally, 18 of the souls would receive the first tier of one of the Achievement the first reincarnated soul had achieved. Each Achievement would be given to two different souls. The god hoped that receiving certain Achievements early would push the newly sapient Dungeon Cores in the right direction.
Lastly, the god granted all of the world's Dungeons Universal Language. The new Law would ensure communication was at least possible between people from different cultures. With everyone speaking the same language, there would be less misunderstandings and a bigger chance of peace.
The god mourned for a moment that they couldn't make Universal Language a Law throughout the Surface world. While they didn't have the energy to do it at such a large scale at the moment, it was more so because Universal Language only worked if you had a language to translate. And if you didn't know a language yet, you would hear only sounds and never a single word.
In short, it would make it impossible for babies to learn a language. Which would defeat the purpose of giving sapients the option for good communication.
With Universal Language a Dungeon Law and the final soul placed in an octahedron and crystalline body, the god could once again rest. This time, confident their world would be okay.