Superpowers.
They were the thing that formed the subtle driving force of the Eternal universe, and in some ways, even the home universe.
People of both universes sought them and craved them, though less than a zillionth of a decimal point percentage of both universes could have them. In a wide universe with numbers so large that even a powerful AI forced to do a census would break down, the number of superpowered users might not be more than 20,000.
Of that small number, many would never cross the F Rank. A few who were lucky enough to have some talent might hit the E rank in the small time they were given in the Black Land. Even fewer would be like Dante and hit the D rank, and that was for the exceptional ones who spent every moment they had in the Black Land fully focused and hard at work.