Sexual slavery is a process wherein someone 'forces' by varied means someone else to engage into sexual activity of some sort.

The mentioned 'force' could be outright force/coercion or be part of an agreement between a dominant and a submissive.
The means are varied and numerous, some not exhaustive means are blackmailing, hypnotism, mind breaking and sexual violence or some form of consensual slave contract.

There are two distinct forms of sexual slavery:
1. A non-consensual one, an act of performing non-voluntary sexual activity due to coercion.
2. A consensual one, usually in some form of a dominant person owning a submissive person as property.

In the environment of visual novels, mainly nukige there has to be postulated a third form of sexual slavery:
3. A semi-(non-)consensual one, wherein the 'submissive' has first to be persuaded by the dominant person by means usually regarded as a criminal act in real life. The Japanese subculture has defined the word 調教 [choukyou] for this, which literally means ‘to teach an animal to do something or to behave correctly’.

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