Zechs, despite previous scenes to the contrary, was not a pervert. The buying and selling of human beings for the sole purpose of sex and sport disgusted him, more so once he was a part of it. He was, however, the older brother of Relena Peacecraft, the ruler of a small but powerful nation called Sanque. It had been rumored for many years that the high-ranking officials of Sanque and her neighboring nations, along with the highest ranking leaders of the colonies, ran an inter-planetary slave trading ring. It was also rumored that this ring of slave traders gathered for a few months every year to trade slaves, compete in slave-games, and gamble on the slave games in a tournament known as Collar.
Up until only a few months before, Zechs had never given any thought to the rumors. Though he well knew how cruel humans could be, he had never truly thought such a large organization could exist without ever being reprimanded by the people or others in the government. It was only when the head of Preventers, Une, had called him in for a special assignment that he realized for much he had underestimated the power of political status.
Sanque itself was a pacifist nation, so held no military or real political power. However, it was also home to the Preventers, an independent military force dedicated to keeping peace and justice throughout the solar system. Une took her job very seriously, and once she heard what kind of games these people were playing she immediately decided that something had to be done.
The only problem was that she needed someone on the inside. She needed someone who wasn't already corrupted in favor of the enemy, while also being in a position of enough influence to interest the enemy, while also having no political position that would be in danger were he discovered.
Zechs knew as soon as she explained what she needed that he was the only person able to take the job, and accepted it readily. Zechs knew the horrors political corruption could cause, as his home had been destroyed when he was young, and his country had almost fallen to ruin. Left to fend for himself for the most part of his childhood, Zechs joined a group of military radicals when he was still very young, under the tutelage of the commander Treize Kushrenada, a boy only a few years older than he and from a very powerful military family. Zechs fell in love with his mentor, and in his teens the two became a couple.
It was not long after that when Zechs discovered his true origins, as a DNA scan at a hospital where he was being treated for an accident in a fencing match revealed his true identity. Milliardo Peacecraft was a name that he vaguely recognized, but quickly accepted. His sister, Relena, was overjoyed and immediately attempted to set up his coronation and return all the power that would have been his, but Zechs refused. Having stayed so long in the military, Zechs didn't think that he would become a very good kind and, seeing how well his sister was running the country, decided to let things be. This created a situation in which Zechs, the once-thought orphan, came into a large amount of wealth and power, but very little political sway. This new personal freedom of Zechs' cause him to look more deeply at his life. He soon found that Treize was not the person he had thought him to be. Zechs decided that he no longer wanted to be with Treize and quietly broke the relationship.
With nothing left to do, Zechs joined Preventers as an agent and consultants hoping to put some of his skills to use. He was able to conceal his identity by using his given name, Milliardo Peacecraft, at social functions and his assumed name, Zechs Marquis, at Preventer's functions. He also wore a heavy mask when fighting or infiltrating. Soon, he was being asked to train new recruits and plan military operations, as well as advising Relena on how to keep her country safe. Zechs was given the title of commander, though he didn't have an actual, documented position anywhere in Preventers. He was, however, highly respected by all other agents and considered one of Une's best men. Still, nothing he had seen had prepared him for pulling the young, almost naked, collared boy into his empty house late one evening.