When it comes to the Master and Apprentice of the Keyblade relationships, they use terms that usualy describe family members to describe the relationship between these wielders.
For example, apprentinces training under the same master refer to eachother as Brother or sister. MX uses this to describe the relationship between him and Eraqus since they were apprentices under the same master, therefore he calls Eraqus "brother". MX also refers to Ven and Terra as being like brothers. And even Aqua remarks to Ven and Terra, "You two would make the weirdest brothers"
Meanwhile an apprentince may refer to their master as being like a father or mother to them. Such as Terra does to Eraqus, he sees Eraqus as a father figure, in turn Eraqus sees Terra as being like his own son.
