Being tied up and restrained
Bondage is the practice of consensually tying, binding, or restraining a partner for erotic, aesthetic, or somatosensory stimulation. A partner may be physically restrained in a variety of ways, including the use of rope, cuffs, bondage tape, or self-adhering bandage.
Bondage itself does not necessarily imply sadomasochism. Bondage may be used as an end in itself, as in the case of rope bondage and breast bondage. It may also be used as a part of sex or in conjunction with other BDSM activities. The letter "B" in the acronym "BDSM" comes from the word "bondage". Sexuality and erotica are an important aspect in bondage, but are often not the end in itself. Aesthetics also plays an important role in bondage.
These stories all contain some form of bondage.