My sister’s anus belongs to me. One day, a brother who is aroused by his sister’s ass secretly creates a mysterious liquid in his room. It is an amazing liquid that increases the sensitivity of the mucous membrane by several dozen times. The brother sneaks into his sister’s bedroom while she is sleeping and injects the liquid into her anus. The sister, whose anal sensitivity has increased without her knowledge, feels strange, but becomes addicted to the pleasure of anal sex. Getting carried away, the brother even prepares an IV drip and injects a large amount into his sister’s rectum. The sister’s ego collapses after the ridiculous amount is injected into her anus. She goes crazy with pleasure during anal sex.