Steven Den Beste comments on the logical problems raised by the fuuzetsu (“time-stop seals”) in Shakugan no Shana. When time stops inside the seal, does it also stop outside? Either way seems to create impossible paradoxes. Either way no one should be able to enter or leave the sealed area.
Of course these problems also occur with any of the other anime and manga series that use a variation of this concept. It’s a convenient notion. Seal off an area where the good guys and bad guys can fight it out, then clean up the mess before anyone notices. The idea dates back at least to X, and also appears in The Melancholy of Haruhi Suzumiya, Pretear, Kyoshiro to Towa no Sora, and who knows how many others. They all are subject to similar critiques.
However I think that in the case of Shakugan no Shana all of the paradoxes can be resolved rather simply by applying the rules of that fantasy universe. Entering full-geek mode, I will attempt to do so. NOTE: This is going to require some spoilers, so those who haven’t seen the series should read no further.
Lets review the assumptions of the series: Certain people, called “unrestricted masters” (jizai shi) can use “power of existence” (sonzai no chikara) to perform “unrestricted methods” (jizai hou). Unrestricted methods are “unrestricted” in the sense that they can violate any of the normal laws of nature, yet they operate in a way that keeps most people unaware of their existence.
For example, suppose that I were to use an unrestricted method to transform the Empire State Building into a giant carrot. Most people would not notice that anything unusual had happened. They would remember that there had always been a giant carrot there, and they would be able to point to history books and old photographs to prove it. Scientific journals would have old articles explaining how it was possible for a giant carrot to grow there.
Things would be different for my fellow unrestricted masters. They would remember that there used to be a building there and that they had seen me change it into a carrot. However they would not be able to produce any physical evidence such as photographs to prove it.
The effect of an unrestricted method is to alter reality to make the change seem a natural part of the universe. (The downside is that if too great a change is required, reality will not be able to adjust and the universe will be destroyed.)
Only the minds of those who know “the truth about the world” will be unaffected. These are people who through training, a magic spell or possession of a magical item are aware of the effects of sonzai no chikara and have some degree of control over it.
So how does a fuuzetsu work? For ordinary people trapped inside it time appears to stop (hence the name “time-stop seal”). For people outside of it time does not stop. Consider: while Margery battles Friagne inside a fuuzetsu, Kazumi visits a museum with Yuuji and watches as he talks with Lamies. Yuuji senses the creation of a fuuzetsu, has lunch with his mother, then walks to the fuuzetsu to see the end of the battle.
Ordinary people go about their business unaware of the fuuzetsu. For reasons that make perfect sense to them at the time they never cross into the area that it covers. If they happen to leave a companion trapped inside the fuuzetsu they will not notice this, but will manage to be back at the right location to meet them when the fuuzetsu is dissolved. People inside and outside the fuuzetsu should be able to compare notes and discover a gap in their memories, but they never do because their memories are adjusted to cover up any discrepancies.
For those who know “the truth about the world” things appear very different. They can see the fuuzetsu as a domed area lit inside with reddish light. They can walk up to it and walk into it. The ordinary people inside will be frozen like statues, but they will be able to move around in it and (if they have sufficient power) perform magic. For them time never stops, either inside or outside.
You still haven’t dealt with the problem of edge effect. What happens if, during the duration of a fuzetsu, someone without the power during their normal affairs wants to go to the place which is covered by the fuzetsu. For instance, what if it covers part of a highway. What happens to people — and cars — who enter. Does a car freeze just inside the fuzetsu?
If so, then what happens to the car just after that, which also tries to enter the fuzetsu? Or the five hundred cars behind it?
Part of the answer to the edge effect is that people WON’T try to enter the fuuzetsu, for much the same reason that they don’t notice vanishing torches. They cannot see, or cannot allow themselves to see, anything that would contradict the illusion of normal causality. Therefore they will find reasons to be somewhere else.
Of course this would tend to cause massive traffic jams as traffic that would normally go through the fuuzetsu is diverted elsewhere. (We can even see this when Yuuji is walking toward the fuuzetsu.) However in a typical Japanese city massive traffic jams are probably not very notable.
In some cases it might be impossible to avoid entering the fuuzetsu, such as a car heading right toward it at the moment of its creation with no way to stop in time. In that case I suppose that the car would enter and freeze, while the drivers of the cars behind it would find some reason to turn down a side street.