Generally, someone trying to advance to the next rank would only need to equip the Mana Mark of the rank above their own in the correct slot.
Whether the mark is of the Active type—which are direct spells like the Ice Goblin's—or of the Passive type, with physical or sensory enhancements, or something similar to Clara's support marks, or Attribute marks that change the nature of the user's mana.
Example: Clara's Marks. Her mana is of the ice element.
For each rank, there is an average number of Mana Marks a user can possess. This isn't set in stone, but it's generally the case.
Rank F is usually defined as having 1 to 2 Mana Marks. It's rare to find anyone with 3 or 4 Mana Marks within Rank F. Although there are some, they are exceptions.
Examples of this include Clara and that guy who studies with Lucius in general classes.
That's because their marks were very low-level and didn't provide enough stimulation for the core to level up.
