The core of magic in Sayuri’s world is the magical field, which covers a magically-endowed being’s immediate vicinity and gives a medium for his or her abilities. Outside of a field, magical powers simply have no effect; this means that offensive magic is essentially useless on a non-magical target, though defensive abilities can still be used as the wielder is always surrounded by his or her own field. In particular, the field provides an intrinsic barrier against external physical harm; magical girls have been known to survive falls from skyscrapers, oxygen deprivation, point-blank shootings, and various other things that would surely kill a normal human being. It does not confer protection against diseases or self-inflicted injury, however.
When two magical fields are in close proximity, about ten to fifteen meters, they begin to grow in size and attract each other in a process called magical resonance. Even novice users of magic can typically detect other magical beings nearby through these fluctuations. Highly experienced magicians can suppress some of the resonance at longer distances by manipulating their own fields, thus achieving a limited degree of stealth, but in close quarters it is virtually impossible to go undetected.
Two resonating fields will eventually become close enough to touch, creating a conduit for offensive powers. Once formed, this channel is relatively difficult to break; especially tenacious one-on-one fights have been fought at distances of over thirty meters. In addition, the strength of magical field resonance increases proportionally to the number of fields involved, such that the linked fields of five or six magical beings can easily cover the entirety of a soccer pitch. Those concerned about collateral damage, needless to say, try to avoid large battles at all costs.