This is postgame thing, make sure you have beaten the game first.
Spoiler
Go to Sanzu River, there's a shack in there with a bed. If you have the Butterfly Dream Pill (Which you can buy from Reisen in the Human Village) you can go to another Dream World. This Dream World is Hecatia's Hell, the haven of level grinding. You'll meet Hecatia and Junko, and Junko can heal you. There's a tower there, you fight 3 Hell Fairies and Clownpiece as your final opponent. After you beat Clownpiece, Clownpiece will be outside of the tower and can offer you to change the levels of the Hell fairies. She can set the level to Lv70 or Lv95. Now you can go to the tower, beat the hell fairies, and go back and repeat.
It is entirely possible to solo the first level 95 fairy with at least one of the following:
Spoiler
Speed Gengetsu@Art of Combat with Thunder Cut/Ephemeral/Evil-Crushing Arrow/Earth Sign, or some Extra Reimu set that a friend of mine uses. Both of these have the advantage of not beng reliant on multi-hit. I also had an Extra Satori set that could do it, but it required using a charm to survive Gigantic, and was a lot slower due to Protean message spam. You need to be base 125 Speed or higher to have a chance at being optimal due to the Speed Remilia, and being level 100 helps a lot too for obvious reasons.