That's nothing impressive, those slow moving bullets aren't made to hit sharp edges like that...
That's not your average iron or stainless steel sword either... looks like carbon steel or carbon steel with some sort of titanium or other reinforcing alloy in the core.
Don't know if thats a Browning M2 .50 cal, it looks like it... Those bullets look more like 30 cal bullets though, so its possible its a japanese Browning 1919, 30-06 machinegun...
If that sword got hit in the SIDE with one of those bullets, it would be destroyed first shot, and you'd see it pierce in the slow motion crap they play it in.
Works the same way as bullet proof glass, if you shot a bullet at it it hits a small point, and thus stays together, but if you throw a ladder at it, it shatters. This is because the impact is spread out. With the blade directing the sharp and strong edge directly at the soft copper/lead bullet, it cuts it in half.
The heat that a M2 or a 1919 puts out, especially after a few rounds, will definitely heat the bullet up VERY hot, and make it extremely soft. The hotter the bore is, the more it increases the bullets temperature, and at that speed makes it like a hard jello. It will still deliver the energy of the bullet, but it will not pierce the sharp edge, thus breaking up or deterring.
I honestly doubt it was the machinegun that was firing at it, theres no way a stock browning M2 or even a 1919 could hit a target as thin as that blade, especially that many times.
Looks cool, but it also looks like a demo of some new sword they are trying to sell the innocent japanese people.
Just my 2 cents!
