Callista was a Jedi from the era of the Jedi purge.  She was a bit unorthodox, but she was brave enough to disarm the Emperor's first superweapon.  She snuck aboard the battlemoon known as The Eye of Palpatine, and after discovering that she couldn't disarm it easily, she tried to use an advanced Jedi technique that would allow her to leave her body and enter the Eye's main computer.  It suceeded.  Thirty years later, the Jedi Master, Luke Skywalker, and his student , Cray Mingla, located the battlemoon in the Moonflower nebula, and over the computer screen, Luke and Callista fell in love.  But Luke had to destroy the moon before it killed anyone, but that would mean killing Callista.  Before Luke could take action, Cray Stunned him and shoved him into an escape pod.  When Luke Awoke the Eye exploded, and realized that Cray had performed a spirit transferrence that put Callista in Cray's body, and Cray died hoping to meet her lover in the after life.  But Luke found that a side effect of the trancefer was now Callista now couldn't use The Force, they traveled from Hoth to Dagobah trying to reverse the effect and in that time Callista found to her horror that she COULD use The Force, the dark side.  She still was a valued addition to the Jedi Academy, and faced down against Daala single-handedly.  When the Knight Hammer  exploded Luke believed her dead, however he recieved a hologram that she was alive.  After eight months Luke and Callista saw each other for a silent moment and parted ways.