Ascend the Tower of Alexandria, taking care to open all treasure chests along the way. You'll need to navigate several floors, often finding switches or pushing blocks to open new pathways. On one of the upper floors, you'll encounter a large, intimidating monster blocking your path. This is a Golem. The Golem is a mini-boss, but relatively straightforward. Focus your attacks on it, using Yangus's powerful physical attacks and the Hero's basic attacks. Keep your HP up with Medicinal Herbs. After defeating the Golem, continue your ascent.
At the very top of the tower, you'll find Jessica Albert. However, she's not in a good state; she's possessed by a dark force, lashing out at her surroundings. After a brief cutscene, she'll attack you. This is your first boss battle against a possessed human. Jessica, in her possessed state, uses powerful Frizz spells. Focus your attacks on her, but be prepared to heal frequently. Once her HP is depleted, the possession will break, and she'll regain her senses. After a heartfelt conversation and learning about her brother's death, Jessica will reluctantly join your party, adding powerful offensive magic to your arsenal. With Jessica, your party is now complete for the early game.