She is the Sailor Moon from Bishoujo Senshi Sailor Moon. Princess Serenity was a lady of grace and beauty. Her mother, Queen Serenity, raised her well to be the future queen of the Moon Kingdom. It was forbidden to have contact with the Prince of Earth, Endymion, but she fell in love with him helplessly. Now, in the present, the two are reunited in a fierce situation.
When Luna, the Queen's old feline advisor, found the Princess, she mistook her for someone else. Not knowing she was right in front of her, she sent this girl out on a mission to find the lost Moon Princess. The girl she sensed power from was named Tsukino Usagi. Luna's mistake was not in vain; she transformed Usagi into the Pretty Sailor Suited Soldier, Sailormoon. The awesome Sailormoon defeated or healed all of her enemies.
At first, Usagi couldn't very well handle being a super-heroine. Her cowardness didn't help her much in battle, but luckily, she had the mysterious Tuxedo Mask to save her. With practice, the unfit teenager turned into an all-powerful warrior. With the new challenges she faced almost every day, Sailormoon's powers increased.
As a school girl, she didn't do well. Her grades were low, she fell asleep in class, and most every day, Usagi was late for school. Somehow, this clueless young lady survived and graduated to the next level of learning. In other words: high school. Being a Sailor Senshi certainly helped her there. With the coming adventures came the strength and confidence that she would need.