Fergason:
Good! Now, to get Petra, you must defeat Beggar Zofan, Zofan, Young Zofan and Engineer Zofan, and take their Petras away. Then you must deliver 20 Unstable Petras to Aku located on the 1st floor of the Seed of Hellfire in the Southern District.
And one more thing! You can go to the 1st floor of the Seed of Hellfire in the Southern District through Transportation Assistant!