Let me start by saying that this is legit, and not cheating.
I found two ways to farm for *Rai* in Phoenotopia. The first one is pretty slow, the second one is the quick one.
Method 1. You must have access to ~Atai City~.
1. Go to the ~Duri Forest~
2. Fill your inventory with *Duri Fruits* by knocking down the spiny fruits and whacking them. There's a small chance that it will drop a *Duri Fruit*. The rest of the time, it'll give you a seed that heals for 3.
3. Take the *Duri Fruits* to ~Atai City~, and give them to the *Duri Fruit Merchant*. Can't miss her, just go left. She'll buy them for 15 Rai a pop. You'll notice this is 5 Rai less than what she's selling them for, for obvious reasons.
This method takes a while, but when you need money, you need money.
Method 2. You must have access to ~Daea~ and the ~Wall~ (cross the ~Misty Gorge~ to get there), this will take a while to get, so get comfy.
1. Make sure you have a *floatation device thingy* (you can buy one at ~Misty Gorge S~ from the *Fisherman*)
2. Go to ~Duri Forest~, and bomb the entrance to the cave. Obviously, you have bombs by now. If you don't then you either glitched the game really bad, or cheated. Why are you bothering to get money legitimately?
3. Go through the cave, and at the end, you'll find a special orange fruit (*S.O.F*). I forget what it's called, but it's important, so grab one.
4. Make your way to ~Atai City~, and go into the building where the woman who sold you the *Truth Potion* resides
5. Talk to her a few times until she asks you to get the *S.O.F* you just got from ~Duri Forest~. You may have to exit and re-enter the building a few times to trigger this.
6. Give her the *S.O.F*, and then exit, and re-enter the building. A new potion will be available. Like, *Fragrance Potion* or something.
7. Buy said potion. If you don't have enough money, use method 1 to farm for some. You should be able to buy it with just 2 *Duri Fruits*, cause I think the potion costs 20 Rai.
8. Head over to ~Daea~, and buy a *Sandwich* from the upper level of the Shop. Easily found thanks to the sign that's right in front of the door that says: Shop.
9. Go to the ~Wall~, and find the save statue. Give the *Sandwich* to the guard to the right, then enter the room on the left, and give the *S.O.P* to the first guy you come across. The *Sandwich* is because the guy is hungry, and he'll reimburse you exactly what you paid for the sandwich. The *S.O.P* is a bug repellant, and the guy is having bed bug problems. I think he gives you a heart gem or a moon stone for it.
10. Exit the room, and go up the ladder to the left. Now talk to the guy to the right. He will have heard of the help you've been giving (see step 9), and ask you to send a *Letter*. A new location will be revealed on the map.
11. Go to the new location (~Farmer's Block~), and enter the first house, talk to the old man, and he'll ask you to exterminate something in the basement. Go down there and kill the frog, and return to the old man. He will give you...
* A Lucky Belt *
This item is also part of the "Most Dangerous Arsenal" Medal. So there's that.
12. Giving the letter to the mom in the next house is optional. You can get a few bucks out of it, though.
13. Go back to ~Atai City~, and find the Shop. It's easy to find, because the building is marked "Shop". Just like in Daea!
14. Make your way to the top level, and talk to the merchant, she will tell you about a "gold exchange"
15. Buy a *Gold Bar*.
16. Sell the *Gold Bar* back to the same merchant you just bought it from, and she'll buy it for, like, twice the price. The *Lucky Belt* is working its magic.
17. Spam and repeat until you're satisfied. I got 3000 Rai out of this, and could have easily gotten more if I was more patient.
No more money problems! You can also get the 999R blood ruby in the ~Hidden Village~ for the 'Most Dangerous Arsenal' Medal as well. To get to ~Hidden Village~, you have to collect 30 moon stones, and give them all to Fran at her laboratory. If you didn't save that Green-haired girl at the Atai Bridge, go save her! Talking to her after saving her reveals the location of her map, and after giving her 30 moonstones, and leaving, then coming back to ~Fran's Lab~, a teleporter inside her lab will be active, and it will take you to the top of the cliff in ~Forgotten Forest~. This area is rather difficult, and you must traverse it, as well as find three keys to get to the Village. Inside the village is a shop that contains said 999R item, as well as a 300 something Rai *Fairy Bottle* thingy that will act like a bottled fairy from Zelda: OoT. You can only carry one at a time, so make sure to get one before going into the pit / other extremely dangerous areas.
While I'm on tips, there's a secret move you can do that's basically a nerfed version of a glitch from earlier versions. What you do is charge up a hit, and then mash the attack button after releasing it. You'll get three Ki-charged hits in, doing a lot of damage. This helps tremendously with bosses, especially if you:
Go into the Well under ~Atai City~, activate the two switches, use the spear to climb up the ledge in the next room, and go forward until you see a bunch of sentinel towers. Then go into the area where there's a bunch of rocks, blow them up, and go inside for an area similar to the final area of the game. Fight through the waves of golems to get a Ki bracelet thing at the end. It will makes your Ki charge much faster than before.
You can also make your spear explosive by getting a Duri Fruit, and a Chocolate Shake, and giving them to the memory-loss girl in ~Crossroads Inn~, followed by giving her your green bracelet (so you have to talk to Thomas to get that pesky golem head out of your inventory). She'll remember you, and return to ~Panselo Village~, but before she leaves, she'll give you an explosive spear scroll. You'll be able to charge up the spear, and it will do much more damage when charged. You can also use it like a bomb, by hitting the tool key again after throwing a charged spear--the spear will explode. Combine this with the previous tip(s), and you have a power house on your hands.