mmm ..... relativity .......

@hinatacretu: not antimatter in the traditional sense (which has a measurable mass), you'd need something more like un-matter. In light of quantum mechanics and grand unified theory though, it's a fun exercise to reduce everything to waveforms and unify those waveforms into a single "thing" -- like a single substance, a wave which is its own medium so to speak. Unifying theories like this would mean that ultimately whether light is the fastest or something else is the fastest, the reason nothing can move faster would be related to the fact that everything is made of the same stuff, including light. Ya follow?

As far as the whole summoning thing goes, I prefer to think of it less as instantaneous movement, and more of being really quick and opening a wormhole-like gateway. So you get your tunnel set up, and the summon reacts and steps into the tunnel, and since these are creatures made for this very purpose they're really good at what they do. This makes the instant of summoning functionally instantaneous, but doesn't too terribly break any laws of mechanics too much.

Of course, the question then arises .... why are we worried about the laws of mechanics in naruto (which is admittedly a ninja-fantasy-adventure type CARTOON) and yet willing to accept the equally implausible bits in mecha anime, or the even more implausible mahou-shoujo genre as a whole? I don't think this merits the brainpower that's already been put toward answering the question, ya know?