At the end of the game, answer all of Fou-Lu's questions 'Maybe so...'. You will be merged with Fou-Lu and will play as the Infinity Dragon (Fou-Lu and Ryu God form). Then, just wipe out your ex-partners to get the ending.
Healing with apples:
When you go into the woods to find the mayor, you have to use 'apples' to lure out an animal. If you run out, find the tree that the man told you about where you can find more. Use Ershil's personal action and head butt the tree. An apple will drop down. The apple is a great healing item for early in the game, healing 100 HP. This may not seem like much, but if many apples, they work well. Stock up to get a full 99.
Go to the question mark west of Fou-Lou's Temple. Go to the area where there was a burning forest. When you fight a Gold Gang and kill it with physical attacks you will get slightly over 1,000 Zenny. If you want even more money, kill it with magical attacks for over 10,000 Zenny. Repeat this as needed.