Steven posted his promised discussion about the physics of Touma’s Imagine Breaker power over at Chizumatic. It’s very spoiler-filled, as is my response below. It started as a comment, but just kept going. I don’t know how to characterize it; it’s not exactly an agreement, nor is it a rebuttal. I’m just killing a few more catgirls by pointing out some implications in the worldview. Below the fold, since there’s spoilers.
Ok, if you take the name of Touma’s power, and assume that magic is “externally powered reality alteration” as opposed to a psionic’s “internally powered reality alteration” then it makes sense that Touma can cancel magic as well as psioncis. It doesn’t require a 3rd power type, which is what I was postulating (from lack of a better alternative). I felt that was a “messy” explanation, but didn’t have any other that could explain how his power worked.
Unfortunately, based on this explanation, it’s theoretically possible for someone to generate an “altered reality” (that is, use a power) that is greater than Touma’s ability to cancel it. Logically, such a someone would probably be the source of the external powers; that is, an angel or other such magical source. After all, we see an angel’s power cause changes all across the world (President Kuroko, lol!). What level is that power? Yet Touma wasn’t affected? In brief, would such beings be subject to the same limits as human beings? Probably not. It just may be that Touma’s not met a magic user strong enough to channel that much power from an external source. If he meets the source directly and depends on his power, he might be in for a nasty surprise.
A possible inconsistency: We twice see ability users devastate areas measured in hundreds of square feet, but Touma not only shields himself, he protects a cone shaped area immediately behind and to either side. Also, he negates Mikoto’s iron sand-swords all the way back to her hands. In other words, the power has to touch him, but once it does, he has an amorphous area of effect that extends beyond skin contact.
What are the implications for magically or psionically accelerated objects tossed at him? If there had been a glass counter between him and the Graviton Bomber, would he have been cut by the flying glass?
As Steven pointed out,Touma is not immune to swords; nor was he immune to having a subway collapsed on top of him (a fate he narrowly avoided). Yet he was immune to having a summoned car dropped on him? Does that mean the substance of the car was inherently magical?
I still believe he is not immune to a railgun shot — but only assuming he is beyond the end of the field Mikoto generates to fire the coin. If she generates her field all the way through the target (him) to guide the coin (likely, given her accuracy with such an aerodynamically unstable object), it would fail the instant the field touched Touma, before the coin began to move forward.