The mission in question is called The Secret of Daikizo Mine. This is a quick mission focused on a couple of cutscenes, so you can beat it in about a minute and a half if you’re quick. After your initial run of this level, you’ll get 300 XP for beating it, plus another 150 XP for getting an S-rank. Now, if you do things right, you shouldn’t need to bring anything or even interact with a single enemy while doing this. If you get seen while practicing, even that shouldn’t bring you down to an A-rank, so don’t worry.
Once the level starts, you’ll want to stick to the high ground to move quickly. There’s a shrine in front of you, so land on top of that and make your way towards the front of the mine. There are archways you can teleport to above the entryway, so stick to those. The only thing to keep in mind is to watch your stamina. The best way to get a feel for this is to simply try it yourself. Just keep to the high ground and you won’t get seen.
How to easily farm experience in Aragami 2
You’re going to want to move to the location with large blue crystals at the back of the mine. There are more wooden beams to teleport yourself to on the left, so do that and then double jump and dash across to make it to the blue crystal area. Watch your step when descending into the area with all of the stone Aragami, as you can get hurt, so aim for the platforms. Then just run towards the center of the room. Skip the cutscene and run straight through the blue crystals, climbing up the steps you just descended.
Now, simply head back to the entrance of the mine. Regardless of what you do, pretty much everyone will be dead, so just head straight on, but there are enemies near the entrance. Crouch and dash to get into the area that’s fenced off near the entrance, and no one will see you. Then double jump and air dash before teleporting to the wooden beam in the entryway and you’ll start a cutscene. Without practice, this might take a little longer than expected, but it won’t cause much issue after a few runs. Do this a few more times and you’ll have yourself a shiny new upgrade point from all that Aragami 2 experience farming.