In the first stage (Akbar) there are four guest rooms in Areliano's house. Faith leads Rahma to the last one to continue the story, but there is a cheat you can do prior to this on the three other rooms. From the stairs in the house, open the doors of each numbered room a set number of times to do the cheat.

1st Room from stairs: open 3 times, close 2 times.
2nd Room from stairs: open 6 times, close 5 times.
3rd Room from stairs: open 9 times, close 8 times.

If you open/close a door over the limit, the code is invalid and you will need to restart from a checkpoint. If done correctly, a sword will appear on Rahma's back and his weapon inventory will have 99 pistols. Although the sword will change into the secret sword found on Akbar upon completing the level, the pistols are kept in the inventory, making future combat easier.

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.