Its simple, Runes are run on the belief that they are the medium to affecting the real world, thus there are collectives of people believing that it would work as it does, and thus, it allows the runes to take the effect that a person's imagination is able to do so. Of course, a limitation is that Runes are set-effects as people need a consistent belief in what that rune does, so it is much more limiting in that sense, but you can simply create whatever runes you want as long as you have a collective belief in it. These are called "Wills"

Description: Rabbit