I guess the most disappointing thing about a film called Satan's Slaves is that it's really just another ghost/hauntings flick. In twenty years time, many Asian horror films still haven't really moved beyond Ringu. While the story itself tries to incorporate some novel influences, the horror is just shrouded ghosts and pale faces.
Rini lives with her family in a remote village, where they take care of their sick mom. When she dies strange things start happening around the house and Rini begins to suspect her mom has kept something important from them. When grandma suddenly dies and the youngest of the family becomes the target of violent hauntings, everyone's in a panic.
Satan's Slaves is a well-made film, the problem is that you've probably seen it many times before. Performances are solid and the cinematography is stylish, but the haunts aren't all that scary and the backstory never really comes into its own. Certainly not bad, but it could've done with more original lore.