Ok, as far as I know, this is in the future....
It first starts out when Relena notices Heero Yuy, a mysterious yet handsome boy...which eventually attracts Relena's attention (what girl wouldn't?) and the rest goes on...we later get introduced to the other pilots..Quarte Raberba Winner, Trbut finds out she is of Peacecraft heir; Heero is the gundame pilot (the main one)owa B arton, Wufei Chang, and Duo Maxwell.
At first, each pilots distrusted each other, but gradually they learned how to get along...kind of..and as for Relena, she obviously likes Heero..and I guess Heero likes her back...since they call each other's name out so much!
Oh, um, let me get to the plot..basically, generations ago, people wanted a cool future so they headed off to space. But the OZ and the Federation formed, gradually using more and more military actions on the colonies. When the series starts, there's this Operation Meteor...but unfortunately, the Federation discovers this...to fight against OZ and the Federation, 5 scientists manipulate gundams like they use in OZ/Federation. It's up to the 5 chosen pilots to stop them and bring peace.