Rain was one of the four android creations of the Keeper. She had the ability to manipulate water.
The Keeper was left by her makers on the Keeper's World to restore it after it was devastated in an ancient war. To assist with this task, and to fend of her loneliness, the Keeper created four nameless android helpers. One of these was an android in female form who could control rain, creating rain wherever she wished.
During the Battle of The Keeper's World the androids sided with Princess Leia Organa, Luke Skywalker, C-3PO, and R2-D2 against a squad of Imperial Stormtroopers. During the battle Rain flooded the Stormtroopers with a torrential downpour, then along with her fellow androids led the Rebels to the Keeper.
Rain had the appearance of a human female with dark, shoulder-length hair. She was not immediately identifiable as a droid, save for her photoreceptors, which looked like a yellow light shining from black eye sockets.
Rain spoke the least and had the youngest appearance of the Keeper's android creations. She did little to speak up for herself, instead either remaining silent, or supporting the ideas of others.
Through some unknown means Rain had complete mastery over her namesake element, being capable of creating rainstorms of any intensity, from a light drizzle to a torrent. She required no atmospheric change to create this rain, and was just as capable of creating it inside as outside.