After you explore the world to find helpful items and skills, you can get some new rings and new spirits for Klarth to contract with.
Cave of Spirits
You can go northwest from Aegis's Workshop to reach Gnome's cave. It's east of Miguel. In the cave, if you encounter Doom Gaze, you should run away. Go to the northeast part of the room and go downstairs. Then go south to the next area. Go south, then as far west as you can go, then north to the next area. Follow the path, then after you cross the bridge, go north and go through the door. In the room with the save point, go through the leftmost door to find a chest that contains the Emerald Ring. If Klarth/Claus equips it, his max HP becomes higher.
Leave the cave, then fly northwest to Bart's old house. Go north into the Long Valley, then go as far northeast as you can go in the area. Enter the cave, and go to the southeast part of the cave. Go down the rope there to reach the room that was filled with Shoki/Miasma. Go east to the save point, then go south and you will see a chest to the left. It contains a Reverse Doll. From there, go south, west, and north above the bubbling pool to find another chest, which contains an Amethyst Ring. If Klarth/Claus equips it, he will be shielded from Earth attacks. Go south, then east, then north to where the path splits three ways. Go east, then north, and you will find a bubbling pool with a boulder in it. Go south from the bubbling pool to find a chest that contains a White Mist. Then go north to the pool, then go east and south to find a chest that contains Iron Boots.
Now leave the cave, rest at Bart's house, and go south to the overworld.
Undine's Cave is on the island north of Venezzia. If the pool in the first room is empty, go through the north door, then go east and south and flip the switch, then skip the next paragraph.
If the pool in the first room is not empty, go east, follow the path, go down the stairs, go south and west across the bridge, and go south, and don't flip the switch.
Go north, then west, then through the north door, then follow the path and go through the door at the end. You will be in a room with two pools. Make a note of which pool is full of water, then go north into the room where you fought Undine, and go to the north end of the room to find a chest that contains the Ice Wall spell. If the right-hand pool in the last room was full, flip the northernmost switch. Then go south to the previous room, and go down the steps in the right-hand pool to find a chest that contains the Sapphire Ring. If Klarth/Claus equips it, he will be protected from electrical attacks.
Now leave the cave. If your path is blocked by water, go north, then east, then south, then flip the switch, then go north, then west, then south. From there, go east, then south, then west to leave the cave and go west from the cave entrance to reach the overworld.
Demitel's Island is southwest of Venezzia. Go to the chamber where you fought Demitel to find a chest that contains the spell Death Cloud. After you get it, go back outside, and go south down the slope, ignore the stairs and go west to reach the overworld.
Important: If you haven't already, you need to talk to the elf at the middle south entrance of Alvanista to learn about Aska.
Fly northeast from Venezzia to reach the island of Thor. You can optionally go into the building to the north, which was rusted shut before. If you sit in front of the counter, you can learn more about the civilization of Thor.
Leave that building and go to the west side of the area, then go south, then east to find the save point. Go north from the save point and go through the corridor. Find the skeleton key as before and use it on the doors until you find the room where you time traveled. Go north to the Mother Computer and ask about Aska. If you don't have the option to ask about Aska, you will have to go back to Alvanista and talk to the elf at the middle south entrance to learn about Aska, then come back here. Then you will contract with Aska after you ask the Mother Computer about it.
Afterward, you can ask the Mother Computer for Medical Treatment. Time Warp is no longer functional. Exit the area, find the Skeleton Key, and use it to find the corridor that leads outside. Go back out to the overworld.
Cave of Darkness
Fly to the continent northeast of Thor that is always dark, and enter the cave southeast of the city. If the cave is empty, you need to go to the Long Valley and get the Amethyst Ring, as explained earlier on this page.
Next, you should go to the Ninja Village.