Celes+/Terra, an AU where Terra remains a soldier of the Gestahl Empire even though she isn't controlled by the slave crown (although some other sort of manipulation might be involved).

Various things that might fit into this idea:
-Terra and Celes might get along easily or they have some sort of rivalry at first
-Terra helping Celes learn how to use her new magical powers (magic!kink is always a plus)
-perhaps the girls grow up around each other, making a romantic/sexual relationship pseudo-incestuous
-If Terra doesn't meet Locke in Narshe and is still with the Empire, when Celes turns traitor, does Terra change sides along with her? Try to rescue her from the dungeons? Remain a staunch supporter of the Empire?

...Uh, anything you like in that vein, assuming you like it (pick and choose)! Sorry this is so long. ^^;