The Current State of Progress
Of course, that was because above the D rank, one could no longer actively absorb Zero Energy to raise the grade of their superpowers. Instead, they had to start 'comprehending' them and the rules behind them in order to progress further, along with fulfilling some requirements for the Zero Energy, of course.
Otherwise, after completing school, those alumni wouldn't care about the Black Land and would only continue comprehending wherever they were. The difference was that in the Apocalypse World, one only needed mutation cores. The superpowers granted here and their growth were based on the real variants, so the person who had this in reality once or currently could achieve the same numbers.
Dante used 10 D Rank Mutation cores to increase the Absorption Superpower to the C Rank.
[Superpower Name: Absorption
Superpower Rank: C