Cless/Cress and the others defeat Demitel and bring closure to Lia.
After the battle, you will be at Bart's house, and Arche will join you.
Arche knows a few skills already, and the rest of her skills are learned from books that you find around the world. Later on this page, there are directions to the spell books that you can reach now. To prevent Arche from casting a particular spell, you can go to her skills menu to disable it.
Arche's tactics are much like Klarth/Claus's. It is recommended to set her tactic to not cast any spells so she can conserve her TP for boss battles.
Bart's House, Part 2
Before doing anything else, use a Rune Bottle on the ?Book that you won after defeating Demitel. Equip it on Klarth/Claus.
Also, equip the Blue Ribbon on Arche, and equip her with an Amber Cloak if you have an extra one.
A suggested formation is to have Mint between Cless/Cress and Klarth/Claus, with Arche above Mint.
Spells for Arche
You can get several more spells for Arche now.
First, if you haven't talked to the mayor of Venezzia upstairs in his house, talk to him now.
Then go to Klarth/Claus's library in Euclid and check the bookshelves. One is in the bottom-right area of the house and the other is in the upper-right corner. You will get a couple of spells.
Then go to Beladum and talk to Lenios. If you met Lenios's twin in Venezzia, you will get Eruption from Lenios.
Now go back to Venezzia. The person who lives next-door to the trading company will sell you two spells. You should get both.
Return to Demitel's Island
You may have noticed that there was some treasure in Demitel's room that you couldn't reach. You can get it now. Go to the northern dock and use the same ship that took you to Demitel's island, and go to the room where you fought Demitel, and open the three chests. The one on the left contains a Halberd, which you should equip on Cless/Cress now. It is better for slicing attacks. The chest in the upper part of the room contains Veggies. The chest on the right contains a ?Book. Use a Rune Bottle on it to turn it into Rabionis, which you should equip on Klarth/Claus now. Rest on the ship, then go back to Venezzia.
Use the southern dock entrance and talk to the captain of the ship there.
Meeting with Meia
On the way to Alvanista, Cless/Cress will have to fight Meia alone. Use Gummies to heal. Meia moves around a lot, so she might run out of the way of your skills unless you time them carefully.