Prologue
Harry Potter knew it was time to move on. It seemed like the universe had stalled all around him. And to an extent that was true.
Harry learned how much more there was the life, to death, to existence when he was 17. It was the day he killed Voldemort for good. It was also the day he mastered all of the Deathly Hallows and became the proverbial Master of Death. A misnomer and huge understatement if anything.
The books about the Hitchhikers Guide to the Galaxy were true, 42 truely is the answer to life the universe and everything. The universe is based upon base 42 math, set in 42 dimensions, of 42 alternate universes making up the singular multiverse. Its easier to just think about the universe currently inhabited as the only one though, it makes the math infinitely easier to understand.
In the universe there are 42 stages of life. Most life is at the first stage. Wizards and witches are just reaching into the second stage. Harry himself was bordering the 40th and 41st. And that is why the universe has stalled. Harry Potter was a 2nd stage lifeform, until he Mastered the Hallows. The Hallows were the 40th stage of a being older than the current age of the universe. Don't look for a detailed explanation on that, time loops and the universe loops as well. Well that will be explained, because it is both where Harry Potter needed to go and what he needs to do.
When a being upgrades its own stage, it requires certain conditions. There are powers one needs to acquire, and events they need to exist through. The 40th stage was one of sacrifice and surrender and addition. The 39th level being needed to give up their life in a way, and Harry had done that by becoming the three Hallows, Harry was an exceptionally strong 39th stage being, thus the three parts. He became the 40th level when he gave up his life as a 39th stage. Then he started to reach 41st by having Harry Potter, 17 year old wizard unite the three Hallows, unite and combine with the power of a 40th stage being. Now the 2 stage being of Potter, it was enough to push it to the line of 41st, combining the soul of the Hallows, with the soul of Harry Potter, transcending both to become something more.
And now Harry, for he identified himself by that name now, and in fact still grounded himself as a human wizard (he suspected this was a part of reaching the 41st stage, to accept that one is still grounded and to act grounded; likely being a good person was a part too); now Harry knew he needed to take the next step to reach the 41st stage. If not for his own advances, but for the universe.
Master of Death just meant he was death. Harry was a part of how things worked, a fundamental force of nature; but nature also worked on those damn cycles and time loops. And because Harry was a 40th stage being, his soul was not changed by anything but himself. But the cycle of rebirth required his soul in particular, it was stuck, and ironically this meant that life had stalled, and people on Earth had reach utopia status. Actually they reached it at about the year 5000, and had continued to live such lives to today, the year 10351.
Harry had taken 5000 years to study this stop. 2000 to reach his conclusions, 1000 to confirm them without any doubt, and 2000 more to find the solution. The answer was as philosophical, magical and scientific, and 39 other things at once. The answer was 42 again.
Harry implemented his solution. He found it is a book in his Gringotts vault. It was a simple ritual, which would actually put a stage 2 being on the path to stage 3. But as a stage 40.9999, it would also convert him to 41st and put him on the path to reach 42. He still wasn't sure exactly what would happen at 42, but his hunch was that he would either become the proverbial God of this universe, taking it over from the former one; he was the god of this universe and its existence was to create himself (take that paradoxes); or he would become the creator of another multiverse, and thus the supreme being there, permanently exorcising himself from this multiverse run by its own 42nd stage being.
All Harry knew was that it was time to start the simple ritual. It would take his soul and reinsert it back into the cycle. The text it was from merely stated that he would end up in his own body, at least one in which he was reborn as. Wizards likely thought they would end up a hundreds years down the line in a decedent's body; that was what the text implied. The base 42 math and arithmancy, it told a different tale, hence the 2000 years to finalize this as the solution. The math said that one age of existence would come to pass, and Harry would be put back into the pattern of life. It would work off the soul of Harry Potter, as it was before his transcendence.
The math also defined the path he must take as a 41st level being. He would need to do this 42 times. And if Harry wanted to take 2000^42 years to do the math, he would be able to confirm his hunch that he would need to do it 42 times in all the other universes in the multiverse (42 dimensional math covering 42 universes was really, really hard and lengthy). But at the very least, he would rebirth himself 42 times. At least with the ritual, and his 40th/41st stage of being, he would not have to experience birth and childhood again, it would insert him into life at a point of critical development, whether for himself or the world around him.
Thus Harry Potter, started the ritual. The planets were aligned, he forced that himself, just to avoid waiting thousands of years for a natural alignment. It was the spring equinox, and Harry stood on the spot where the last person to use this ritual performed it, where the Veil of Death stood in the ministry (his memories were a little old and fuzzy, but he thought that the Veil was something he created as a lesser being, either just because or possibly as part of the transition to a higher level of being; it certainly felt like something he would do).
Harry dripped blood into the runes he carved, chanted some rather guttural sounds, and as the winds and pressure and power reached a crescendo the Veil stopped all movement and morphed into something a little more gaseous. A second later, Harry walked into this mist.
And life moved on.