Boy Love Aficionado: Achievement PSN of South Park: The Fractured But Whole

See: South Park The Fractured But Whole Yaoi Locations (Text Guide)

There are 40 Yaoi Art Pieces. You can get all of them after the story in free roam. None of them are missable. It's better to do them after the story because you need certain abilities to access everything (which are unlocked automatically in the endgame).
The Yaoi art pieces are anime-style drawings of Craig and Tweek. Some are hanging on walls and you need to shoot them down with firecrackers first. There's also a map for their locations in the basement of Bebe's house.