Sorry in advance if it was already stated, next to certain rune slots is a blue or red ball appearing.
What does it mean ?
I noticed Georg's attacks glow in red sometimes, his Killer rune has a red sphere.
Also the Killer rune I attached to the Prince has nothing.
So I thought it was some kind of bonus effects from support / technique runes, depending of the character,
but Sialeeds and Cornelio also have red globes next to the magical Wind runes I gave them and next to the innate DoReMi's one.
Their magic or physical attacks don't show anything so it's pretty unclear for me.