Lotta Brest

Daughter of Dr. Brest, a leading scientist. She has been a close friend of Billy since they were quite young. Not that they're all that old now... She often tags along with Billy, occasionally even resorting to stowing away to achieve this end. You'd think Emely would be able to stop such behavior... She's terribly fond of her "little sister" Myusha.

(Source: Wikipedia)