In an alternate world much like our own people discovered a way to transform people years ago. In order to transform people have to wear special collars. There are a couple of catches with the collars though. The first catch is that the person wearing the collar can't transform themselves. They have to be owned by someone and that person has the power to transform them. This makes them a slave to their master/mistress. The second catch is that once the collar is on it can't be taken off unless the slave's master/mistress becomes a slave themselves or the master/mistress dies. There is a safeguard built into the collar so a slave can't kill their master/mistress. The third catch is that if they don't have any genitals unless their master/mistress allows them too. They just have a pee hole between their legs. The fourth catch is that being without genitals the slave has no sexual feelings. Instead they experience their master/mistress' sexual feelings.
The collars themselves are either baby blue or baby pink depending on if the slave has a master or mistress. In order for the collars to work they need a little blood sample from the master/mistress and the slave.
The slaves hardly ever wear any clothes since clothes tend not to change with the slaves. The only time you'll see a slave wearing clothes is when their master/mistress allows them to or they buy special clothes imbued with the slave’s blood. This is rare though as most master/mistresses want to be able to change their slave on a moments notice and the special clothes are expensive. Slaves are unaffected by heat and cold.
At first there was no shortage of people willing to give up their freedom for the chance to be transformed. Now however that interest has dropped and some slave traders have taken to kidnapping people to fill orders. Turning people into slaves is a serious offense and the punishment for a trader who is proven to have done that is to become a slave themselves.
Of course once someone becomes a slave they're not allowed to work since they remain close to their master/mistress and anything they owned becomes the property of their master/mistress.
Now who do we follow? Will it be a master/mistress or a slave?