Yaoi is a genre of Japanese art, usually made for and by girls, that uses fictional media to create sexual or romantic relationships between male characters. This art form was displayed heavily in the Season Nineteen episode, "Tweek x Craig" and in the video game South Park: The Fractured But Whole as a part of the Scavenger Hunt: The Yaoi Project mission.
Many of the Yaoi pictures seen in the episode were drawn and submitted by South Park fans, at the request of the show's creators.
For a list of Yaoi art from South Park: The Fractured But Whole, visit List of Creek Yaoi Art.
Images of Yaoi art
