Collect all 60 Poe Souls and bring them to Jovani. He is in a house in the southeast corner of Castle Town. Turn into a wolf and dig your way inside. Use your senses to find out where to dig. After you give him 60 Poe Souls he will give you a Silver Rupee worth 200 Rupees. Talk to him again to get another Silver Rupee worth 200 Rupees. Repeat this as much as desired. Then, go to Malo Mart in the Kakariko village. Donate enough money to lower the prices at the Town Castle's Malo Mart. You will now be able to buy a Magic Armor there for 598 Rupees. The Magic Armor makes you immortal, but normally reduces your Rupees until you have no more. Because you can get unlimited Rupees, you can stay immortal.