Ruka

Lucca is Noelle's younger sister, and is an elven-looking creature. She is a mad scientist, and often makes different mechanical devices to help Noelle learn to fly and become an angel. In one of the episodes when she meets up with Eros she gets interested in him because of his speed. When Eros tells her his speed is due to his love for Silky, she thinks it's a silly idea because of her obsession for science.

(Source: Wikipedia)