One common theme is the forbidden love. This could be between different species like a vampire and a human, where the sexual and romantic relationship is not only desired but also taboo. Another theme is power dynamics. For example, a powerful wizard and a novice apprentice falling in love, and the power difference adds an extra layer of sexual and romantic tension. Also, the theme of redemption through love is popular. A character with a dark past finds love and sexual fulfillment in a relationship and is redeemed.
Common themes include transformation. It could be a physical transformation like a werewolf's change during a full moon and how it affects their relationship with their lover. There's also the theme of soulmates. The idea that two characters are destined to be together sexually and romantically, often across different worlds or lifetimes. And then there's the theme of exploration. Characters exploring their own sexual fantasies and desires within the context of a new and exciting romance.
Some common themes are the exploration of new worlds in the context of sex and romance. For instance, a couple travels through a portal to a different dimension where they experience new sexual and romantic adventures. Another is the theme of self - discovery. A character discovers their true sexual self through a romantic relationship. Also, the theme of passion against all odds. Two characters from warring factions fall in love and their sexual passion overcomes all the obstacles in their path.