This character is subject of prolapse.
Prolapse literally means "to fall out of place‚" from the Latin prolabi meaning "to fall out." In medicine, prolapse is a condition where organs, such as the uterus, fall down or slip out of place. In hentai prolapse is usually depicted as a grotesque body modification where the vaginal or anal walls distend out of their respective holes.
NSFW Example 1
NSFW Example 2