"There's still more to do, that's why I need more time."
With a strong determination, the old man picked up his rejuvenation potion. The secret of this particular potion is that it rejuvenates the body while preserving the person's memory. Essentially the fountain of youth. The old man took it anyways and it took a while for the potion to tale effect. Five hundred years passed... The man, or young boy at this moment, awoke and found himself in the same world yet different. Nations disappeared, Regression of Civilization, decline in human skills and even basic alchemy has been lost! Lost Knowledge, Lost Technology! Nothing impossible in the mastery of alchemy!
(Source: SB Creative Corp, translated)