Fire Spring is home to the Major Psychic Psycho, which has a small chance (1/128) of dropping the Star Pendant. You can't get the Star Pendant anywhere else but from Major Psychic Psychos, so try to get one (or more) if you wish. It will take a long time, though, just like with the Sword of Kings.
With Fire Spring you won't be able to return to it for kind of a long time after you beat it, so you might want to go ahead and get all of the treasures from it before you take on the final boss.
For the first item, go into the door that is across from the Fire Spring entrance. There is a Speed Capsule in this room.
Leave the Speed Capsule room, then climb up the rope near the door. Climb up the second rope and go into the room. When you exit from this hallway, you will be near a rope leading down. There is a Bag of Dragonite nearby.
Go back up the rope and back the way that you came. Descend the two ropes and head east. Just past a pool of lava is a door. Go in, and go through the hall. You'll come out near a rope, but head to the right to get a Cherub's Band.
Return to the rope and climb up. Just above the small volcano is a rope. To the left, there is a door. It's a Magic Butterfly room, so use it to heal up if needed. When you're done, go up the rope and into the room for a Horn of Life. Go back outside and down the rope, then into the door to the right.
Go through this hallway, up a couple of ropes, and into a door. Heading left, go into the first door that you encounter and climb up a rope, then down a rope, to get the Moon Beam Gun. Return to the door and go in, then go up and left through the westernmost door in the small room.
Once the boss is gone, you should go to Fire Spring, which should be the last Your Sanctuary! Before getting the melody, be sure to give Ness a Sea Pendant and Franklin Badge, and plenty of healing foods and maybe some weapons that he can use, like Bombs or Bags of Dragonite. When you're ready, go and get the melody.