1. The treasure hunt theme was one route as the character could be after the Nyami Nyami walking stick as a rare relic and also has a connection to the river god who could be conjured by it from the main villain as a final boss in the game, a bit like Uncharted where the treasure at the end turns out to be cursed and has to be stopped before it plagues the world. The legend of the story and fear of it's power could flow through out the game.
2. The other idea I had was looking at the voodoo route as African tribes have a strong belief system of witchcraft and spirits and would tie up the african theme of the game. I have approached this option with a fresh mind today and considered an evil witch doctor that realises a curse of bad spirits that flood through the people and creatures to consume them so that they no longer know who they are and what they are doing except through the control of the witch doctor, Nymaminyami and other African Gods, etc could be bosses within that game where the character has to defeat them to remove the bad spirits and then in return acquire a weapon to help them along their quest so in sense of Nymainyami it would be the walking/ritual stick to be able to control water and weather related powers.
The main hero character could have a healing braclet that shields him from the voodoo which stops him/ her from changing
I think I perfer Idea 2 as that feels it is started to connect more with the African Myth and would well as a platform game but please leave comments with suggestions if anyone has any other ideas to add with this or even improve it.