In the manga of the same name, she is called Rastel. Asbel is her twin brother. She lives through the destruction of Pejite. She flees with the Control Stone for the God Warrior they unearthed, but unfortunately lands in the Sea of Corruption. Before she dies, she gives the control stone to Nausicaä.
In the anime film, her name is Lastelle (wich is phonetically the same to Rastel in Japanese). She is first seen in the Tolmekian aircraft before its crash. Nausicaä rushes through the flames to save her and breaks her chains with her sword. She then tells Nausicaä who she is and that she must destroy the aircraft's cargo. Nausicaä replies that it's burning and, reassured, Lastelle dies from her wounds. Later, the name of Lastelle helps Nausicaä to convince her brother Asbel that she is not an enemy.
Princess Lastelle is a beautiful young woman around Nausicaa's age. She has brown hair that goes a couple inches past her shoulders and brown eyes. She is seen wearing a long pink and yellow dress with a matching yellow hat, with jewels embedded in it and diamond earrings. She was a princess, but after her country was destroyed, she was reduced to a slave with her hands shackled. She then was moved to slave market by Airship Corvette.