Mobile Suit Gundam: Secret Rendezvous

Set in U.C. 0079, during the One Year War between the Earth Federation and the Principality of Zeon. Lalah Sune, a girl who escaped from a brothel in the Ganges River basin, is taken in by the Zeon officer Char Aznable. Char recognizes Lalah's potential as a Newtype and seeks to test her abilities in space. Meanwhile, Amuro Ray, a young boy who has inadvertently become an MS pilot for the Federation Army, encounters Lalah at Side 6, a cluster of space colonies where he has docked for resupply…

(Source: Wikipedia, translated)