Until he was nine, he lived on very little, panhandling and pickpocketing in various cities around the planet. He was taken in by an General in the Tal'Shiar, T'sart, who was in hiding on the planet. He took Rain under his wing and trained him as a spy. He was enlisted into the Tal'shiar and became one of their spies in the outer reaches of the Federation. When T'sart left the planet, he offered to take Rain with him back to Romulus, but he declined, realizing that he could never make it as a human in the Tal'shiar.

Homeless again, Rain returned to his life of petty theft. Once he looked old enough, he realized he could make more money by prostituting himself. From there, he moved up in the underworld, moving from gigolo to small-time drug dealer and eventually became an assassin for a large crime family. By now, he'd become surprisingly rich but knew he was just indebted to the family. In a failed attempt to take over the planet's organized crime, he sent a message to Starfleet informing them about the corruption on the planet. The family was dissolved but Seth was marked for death by its associates. His riches were liquidated and he was left with nothing.

He knew he had to stay alive and figured that the safest place in the galaxy was on a heavily-guarded, heavily-armed starship. At first, he was infuriated having to answer to so many people, but he's beginning to enjoy the fact that he is not constantly in mortal danger. His first mission re-united him with T'sart, this time on opposite sides of the battlefield. T'sart had betrayed the Romulan Empire and was on his own personal mission. Rain's loyalties to Starfleet and the Tal'shiar won out over those to T'sart and he ended up as a double agent on his ship. Even though he knows he did the right thing, he still beats himself up about betraying the man who raised him.

Rain retains his underground savvy, but also a very distrusting personality. He knows that there are hundreds of thousands of people who would love the bounty on his head. He also figures that most people think like he does and would kill him on sight if they knew about the potential money. With that in mind, he tries to keep a low profile. If he wants to be, he can be very charming. Usually, though, he prefers not to be noticed by anyone, lest they recognize him as a former Romulan spy, fugitive, murderer, drug dealer, "rat", or any of the other roles he's played in the past. Seth's hobbies include ancient weapons (mainly gunpowder based firearms) and security systems (as in finding ways through them). He likes to keep up on current events, hoping every day that he'll hear of the fall of another crime family that wants him dead. He immensely dislikes holodecks. In the past, he'd used them to ensnare his targets and knows they could be used against him.