Queen Beryl is the ruler of the Dark Kingdom. Her goal is to awaken the Dark Goddess Metallia. For that means she orders her generals and in extension her subjects, the youma, to gather life energy. This energy is then offered to Metallia.
Queen Beryl is the most powerful fighter in the Dark Kingdom and a despotic ruler. If her orders aren't met with success she has no qualms imprisoning the perpetrator in a crystal prison.