You start this chapter right after you leave the location with the boss. Fly to the left, where you find Rubella. She will be helping you in fight. The character starts with 6 points to distribute on the skill tree. If you want to train combat with two characters and obtain some more experience, go down. There, you can fight with opponents that you have already killed in chapter 2.
While flying around this location, you can encounter new airborne opponents. They may be demanding if you ignore them. You have to attack a single opponent with both of the characters/ The opponent on the left can speed up his and his party's attacks. If you do not deal with him fast, he will make fighting difficult. Do not bother with shield. The best defense in this fight is offense. This battle will reward you with 650XP.
To proceed, you gave to cross the whole map that you have already explored to the left and pass by the starting point. After you get to the very end of the map, you will encounter the boss. Along your way, you will find many collectibles and kill many opponents. Use this to your advantage. You will need potions and XP later in the game.
After you kill the boss, you will be able to cross the gate. After you do that, you will receive the map of the kingdom of Lemuria. There are new opponents in this location - Golden Griffins. They always fight in the company of spiders or wolves and this tends to be difficult. Still, you will receive a lot of XP after you defeat them. To end this chapter, you have to go left and find a village.