KD Letter Circle, also known as the K9 series, is a role-playing form within the BDSM community that requires Submissive (服从者) to mimic dog behaviors and emphasize absolute obedience and loyalty to their Dominant (支配者). It is characterized by specific behaviors, language, and posture, often accompanied by training elements and aftercare practices to ensure mutual trust and safety.
In the letter circle (letter circle refers to the Sadomasochism community often abbreviated as BDSM), K9 refers to a form of role-playing in which Submissive (服从者) imitates dog behaviors and emphasizes absolute obedience and loyalty to their Dominant (支配er). It is characterized by specific behaviors, language, and posture, and is often accompanied by training elements and aftercare practices to maintain mutual trust and safety.
K9 typically includes but is not limited to: adopting dog-like postures (such as belly-up, tail wagging), using dog-related terminology (such as "sir/madam", "yes"), demonstrating loyalty and seeking guidance from the Dominant, as well as simulating everyday life activities such as fetching items and guarding the house. These behaviors are not a regression to primal instincts but a voluntary performance and emotional immersion within the framework of agreement.
The K8 series is a role-playing form commonly seen in the BDSM community, where Submissive imitates cat behaviors, exhibiting characteristics such as aloofness, pickiness, and possessiveness.

The K9 series emphasizes discipline and training, representing a unique exploration of human-animal relational boundaries within the BDSM community.
For newcomers to the letter circle, understanding K9 and other related roles is the first step toward safely exploring this unique form of role-playing in the BDSM community.