The railgun shell was cut in half and narrowly flew past Lycoris (pg.17)
the trail in pg.18 is the tracer from the shell
Railgun projectiles are generally too fast for a tracer (or even explosive filling like a cannon shell) to be useful; they're generally just metal darts. The trail would be a shockwave of water vapor and potentially molten sparks from the launch rails.
SSStylish! Victory!
It is interesting how some top batters or martial artists can react to things humans per se can't react to with enough skill and practice.
More of knowing where the projectile will be and being there before hand than actual reflexes.
Still, I don't think the sword would survive the hit. Also even if the parry would split the shot, the splinters would hit you most likely still travelling at mach speeds. Is a video game this time, so logic & reality need not boringly apply.
Something I learned from swordfighting is that your arms are slow and your eyes are slower. Intercepting sword swings is half reaction and half intuiting the end result. And yes, if it was working on physics simulation, both katana and Crim are toast.
Cutting an ordinary bullet is potentially possible because they're soft metals: lead wrapped in a copper-alloy. Kinetic penetrator darts are generally hardened tungsten alloys, so they tend to go through things and let the shrapnel and spalling formed from the hole do the damage, only stopping when they lose enough energy to punch another hole, and then smushes or deflects off.
So, what happens if we assume our Crim-crim's magical katana is perfectly hard? Math(s) time!
The US Navy's
experimental railgun used 20kg projectiles at 2,500 m/s (Mach 7.3, at sea level).
Kinetic energy is 1/2*the mass of an object*its velocity squared:
The result is 6.25x10^7 kg*m/s...or 62.5 Megajoules (MJ) of energy. That seems like a nebulously big number, so let's get some context.
1 gram of TNT releases 4184 joules (4 kJ) of energy.
62.5x10^7 J *(1 gram of TNT/4184J) = 14940 grams->
15kg of TNT.
I repeat, the railgun projectile slams into Crim's sword as if a bomb with 75% the mass of the railgun dart was taped to her sword, then exploded.
And then Newton's Third Law comes into play: "If two bodies exert forces on each other, these forces have the same magnitude but opposite directions." The sword pushes back on the railgun dart and splits it...but the sword also inherits much of the momentum of the impact.
The two halves of the railgun dart deflect off at angles determined by the exact point of impact and the angle of the blade and the impact angle of the railgun dart, but each is going a bit slower, likely closer to 2200-2400 m/s, with 3-10% of the projectile vaporized into tungsten shrapnel that impacts poor Crim in the roughly .4 milliseconds (400 microseconds) it takes the shrapnel to travel the roughly 1m distance from her outstretched arms. The sword (now moving close to 2000 m/s, depending on angles and how much both sword and dart deform/deflects), fragments of her wrist bones, and the shockwave created from the collision of the dart and the sword all hit her vitals within about 25 milliseconds, give or take.
tl;dr: Crim surviving the parry is total game mechanic, because she's basically parrying a carbomb going off at arm's length.