I Have an Unreliable Devil System

I traveled through time and became a demon king. Before I could enjoy the life of a demon king, demon-slaying warriors came to destroy me. Fortunately, there was a demon king system to help me. But why is this Demon King system so deceptive, and why does it want to defraud me, the host, of its 'money'. This is a funny daily routine where an unreliable system helps a young man become a devil.