Metal Gear Rising: Revengeance walkthrough: VR Mission 004
VR Mission 004 is fairly easy to find, but it's also easy to miss (like the majority of the VR Missions). Proceed through the Refinery in File R-01 until you reach the stack, where you fight Mistral. Before you head up the stairs to the top of the stack, check for a set that descends. These will lead to the computer console containing the VR Mission.
You're pitted in another battle sequence this time, but you have to kill your foes in a unique way: each kill must be a Zandatsu kill. Take them out normally, or fail to use Zandatsu during Blade Mode, and you'll fail the mission. There are regenerating Electrolyte Packs scattered around the area for you to recharge so you can reliably use Zandatsu, but if you fight correctly you won't need them.
Your first battle is against a run-of-the-mill soldier. This fight is a piece of cake. Let him run at you, parry, and slice into him. If you time this correctly you'll get a Zandatsu notification after he's stunned, but it's faster to parry and go straight into Blade Mode to slice him up.
Your second battle, by far the hardest of the three to pull off, is against a sword-wielding larger cyborg. You've encountered these guys before, and if you know how to pull off a quick Zandatsu kill against it you'll have an easy time. If not… this is where most of your time will get eaten up.
Like all enemies you need to stun these cyborgs to get a proper, quick Zandatsu hit, which is pretty difficult to time. The ideal time is during the three-hit combo he delivers, try to avoid the first hit and parry the second to mess him up, then use Zandatsu to rip him apart. If you really can't get this to work, hit him around normally a few times until he's off-balance and use Blade Mode to slash him up a bit. This will usually stun him and allow you to zip in, rip him apart and perform Zandatsu. Time-consuming, but it will work if a gold ranking isn't an issue. Otherwise, practice your parrying and take him down as fast as you can.
Your third battle is against a Gekko. You need to get a bit lucky on the Gekko, as the easiest way to perform a Zandatsu hit is by parrying the thing when it's rushing at you. Get your meter up to full, wait for it to lower its head, and parry as it charges head-first at you. You'll have to pound some buttons, but when the sequence ends you'll reliably be able to slice it open virtually every time. (This applies to Gekkos you fight elsewhere in the game, as well.) If you're having trouble goading the Gekko into charging, keep your distance - it's more likely to run at you if you're across the arena.)
There's a bit more leeway in this one with a gold ranking at one minute flat. Still, you'll probably have to practice on the second cyborg several times before you can whittle down his time enough to snag top place.