If you are ever needing to gain a lot of EXP quickly, maybe for the Chapter 12 fight or True Final Millennium Tower, then this is what you need to follow. In Yokohama, at Sunrise St., right next to the original Ichiban Confections location, there will be a manhole that allows you to go to the Yokohama Underground Dungeon. In that dungeon, you will find characters called “Invested Vagabonds.” These guys give you about 60k EXP a pop, so very valuable. In the dungeon, fight through of all the fights until you get to the dungeon with only one room, where you fight five Toxic Wastoids. Once you are in that room, turn back and go back up the stairs you just came from.
Now back in the previous dungeon, the enemies will have respawned. The second to last, or since you are going backwards, the second fight in this dungeon will have an Invested Vagabond. Go through the first fight, an easy way to finish it is by using Ichiban’s “Essence of Orbital Laser”, which kills all enemies, then go back to the second fight and take out the Vagabond. Do this by using Joon-gi Han’s Rapid Shot, which kills it. After defeating the Vagabond, do the same thing, going back to the Toxic Wastoid room, then going back to the fight, and repeat. This strategy gives you about 60-70k EXP every 90 seconds, which is not bad.