The secret sword is available after Jabez's betrayal. Once you reach his ship you will once again be able to run about the island. Go to the shop with the cannon outside. Jump on the cannon then into the open window. Inside, you'll find the secret sword in a box.
Enter Areliano's house. It contains three empty bedrooms and a fourth guest room to which you are taken. You must open the doors into these rooms from the corridor in a particular order to enable cheat mode. Opening the doors from the room side will not count -- you must be standing on the corridor side. There are three doors in the corridor, with the third door being the closest to Rhama's room. Open the first door three times, the second door six times, and the third door nine times (in order). If you make a mistake, you must start again. If done correctly, the final Boss' sword will appear on your character's back and you will have 99 pistols in your inventory. Additionally, when you complete the game, all ending credit bonuses will be unlocked. The pistols will disappear when you proceed to the next level. Collecting all of an item after the code is enabled has the opposite effect and will negate that bonus in the ending sequence.
Successfully complete the game to unlock the survival mode and level select options.
Alternate Ending Sequence
Collect all the treasures and secret swords during game play to get an alternate ending sequence.