Realms are the world's in which more than one universe is born. In a realm the main universe houses branches of other universes, that are weaker than it, simply because of the powerhouse that lives in that realm.
Realms are also ranked by the powerhouse it houses. If a realm was an F-rank, then a powerhouse of that realm infiltrates a realm with the powerhouse of an E-rank, and manages to kill the E-rank powerhouse of that other realm, and raise through the ranks of his ability becoming an E-ranker.
When he returns to his original realm, the realm will raise through it him becoming an E-rank from it's original F-rank status. In order for the realm to advance in rank, the powerhouse must be someone of the main universe. If it's someone from the branch universes it won't make a difference.
