The series' general emphasis is on the enjoyment of sexuality as a playful activity. Foglio satirizes numerous plot elements of fantasy and science fiction, such as time travel, cloning, robots, deals with the devil, love potions, and geasa. It portrays a variety of sexual activities, including "oral sex, anal sex, group sex, masturbation, voyeurism, double penetration, inter-racial (literally), bestiality (although generally with an animal possessing intelligence), mild sado-masochism, homosexuality (female, in every issue; male, just in the last issue), exhibitionism, sex with any number of devices, necrophilia (specifically sex with a ghost), prostitution, and various others, including some that were only possible in micro-gravity". Foglio cited rape, mind control, pedophilia, "classical necrophilia", excretion, snuff porn, branding, piercing, heavy sadomasochism, and spanking as topics that he did not find appealing and would not write about. He recalls, "I had a pediatrician tell me if she had a choice between a young teenage boy finding "XXXenophile" and "Batman", she’d throw him "XXXenophile" because it teaches much healthier interactions. Of course, this particular pediatrician would not go on the record, and I would not ask her to, but it still gave me good feelings for the day."