Leveling up party members and equipment in JRPG games has always been something of a grind. Thankfully, however, there are a few shortcuts that can be taken in order to speed things up a little bit in Final Fantasy VII Remake. This bodes well, as not only will you need to reach level 50 in order to take on some of the game's tougher challenges, but you'll also need to fully master a complete set of materia if you're hoping to unlock the game's platinum trophy.
While hitting level 50 is actually something that will occur naturally during a hard mode playthrough, it's possible to do so almost immediately after unlocking hard mode. This method will also provide copious amounts of AP ensuring that your materia will be maxed out in no time as well. All it takes is the right setup and a dash of perseverance.
Location
One of the great things about the hard mode in Final Fantasy VII Remake is that chapters can be tackled in any order, so let's begin by loading up Chapter 17. Make your way back through Hojo's lab until you reach the point where you need to battle some Unknown Entities while Barret and Red XIII move some debris. After heading through the newly unblocked door, you should now see Chadley directly in front of you. Head through the door he's standing next to and you'll arrive at the Shinra Combat Simulator.
Equipment
It really doesn't matter too much who you have in your party, but including Aerith should speed up the process quite a bit. Equip her with an orb of Lightning materia and pair it with your Magnify materia. If you happened to have bought the Whistlewind Scarf from the Moogle Emporium, equip this on her too as well as two orbs of First Strike materia. You should have gotten one from Chadley for completing Battle Intel Report 3 and can purchase a second from him for 5,000 Gil. If you don't have the Whistlewind Scarf, just equip something that will boost Aerith's magic instead.
All of Aerith's other materia slots can be filled with materia that you'd like to master, as too can those of the other two party members you choose to take into battle. As you'll likely want to master a few orbs of Magic Up materia for some of the game's tougher content, it makes sense to slap these on Aerith to increase her damage. If you picked up the Pedometer materia near Aerith's house in Chapter 14, it should have already turned into an orb of AP Up materia by now and so you should pair this with Revive, Elemental or Subversion materia as these take the longest to master. You could also obtain the EXP Up Materia by defeating Team Ragbag in the Shinra Combat Simulator, but you really shouldn't need it.
Strategy
With your party all set up, open up the Combat Simulator and look for the 'Three-Person Team vs. Mayor Is Best' challenge. It's actually the same one you took on as part of the main story so you should already be somewhat familiar with it. Despite being on Hard Mode, you'll be able to select the easy difficulty so do that and wait for the battle to load.
When the battle begins, you should have enough ATB to cast Thundaga straight away, but if not, spam a few regular attacks to charge Aerith's gauge. Depending on your level and stats it should take two or three casts to take both enemies down. It's possible to emerge victorious in as few as four seconds, but most runs will likely take around 10. As soon as the results screen pops up, hit triangle to restart and then rinse and repeat.
Each run will reward you with 30 AP and 1,440 EXP meaning that, after accounting for loading times, you'll be able to earn at least 120 AP and 5,760 EXP per minute (11,520 if you have the EXP Up Materia equipped). There are actually better methods for farming EXP such as replaying the garage section at the beginning of Chapter 16, but if you're looking to level up both your party and your materia, the combat simulator is the fastest way to do so.