Sounds like basic setup for a game. But it's good thing cause it makes story creation easier.
You can have main story either:
A. Michael is tasked by superior being to collect the gems for good purpose. However everytime Michael is about to take a gem, a mysterious voice warns him not to. Michael ignored the voice and resume the collection. After all gems are collected, the being used the gems to bring back his lost power and regain his status as evil emperor of the world. It turns out the gems were his source of power which were taken from him to weaken him and seal him 1000 years ago (cliche).
or
B. An evil group is collecting the gems for their evil purpose. Michael thinks that the best way to stop them is to collect the gems earlier than them. This strategy works except the general of the group realized this and steal all the gems after Michael collected all gems. Michael has to go to their base to get them back.
Which one do you like?
I'm aware those two stories are pretty cliche but we could add twists later if needed ;).