bordemstirs
Member
some gameplay related reason for creating the groups
Rainbow Gravitation is a skill you get from Rainbow's Gravity, which was originally available through the Traveling Trader. So it matches the group above it, which are all the Class Skills that were made available through other items released by him as well.
The sub-column starting with Ballad is Hobopolis-colored, because those items all drop from the bosses in Hobopolis, and their vertical alignment in the last column is because they are are Accordion Thief buffs.