Rain uses the power of water to kill his opponents.
Rain is from the ancient realm of Edenia. He hails as the child of Argus, Edenia's protector. It is currently unknown who his mother is, however Argus's shame of infidelity, caused him to exile Rain from his royal family. As a result, Rain was given to an unnamed, but key general, in the Edenian military. Rain is a demi-god, the son of a true god and a human.
His actions may have began before the events of the 1st Mortal Kombat tournament, as depicted in Mortal Kombat Deception's Konquest Mode. Rain appears in Mortal Kombat: Deception as a non-playable character and is involved in two separate side quests. One of which involves Rain asking Shujinko to retrieve the enchanted dagger of the royal Shokan family. Rain states that Shao Kahn has enlisted him to retrieve the dagger for his own purposes, but Rain actually plans on keeping it for himself. Although this quest ends in Jade knocking out Rain for his troubles, it is can only believed that he did keep the dagger, as it appears as part of his wardrobe in Mortal Kombat: Armageddon.