The Sailor Scouts felt weak because their energy was being stolen by the Cardian. Suddenly, Queen Serenity appeared and gave Serena the Crystal Star Locket and the powerful Moon Scepter. With these new, stronger weapons, she was able to attack and finally defeat the Cardian.
We were almost beaten, but thanks to my mother, the Moon Scepter helped me to defeat the enemy.
From Episode #151 “Cherry Blossom Time”