Level: Bard 6, Hetaera 6
Casting Time: 1 full round action
Range: Same plane
Target: One current or former sexual partner
Saving Throw: None
Spell Resistance: No
This spell instantly brings a current or former lover to your side. The summoning will only work if three conditions are met: 1) the target has had sexual relations with you, 2) the target remembers you, and 3) the target is willing to be transported to you. The target of the spell will appear adjacent to you, in a space you choose. The target must be in an area in which magic can be cast, and must be able to travel extradimensionally from its location to yours.
Many spells can be used for sensual and romantic purposes in D&D. Although the Book of Erotic Fantasy provides spells that are directly sexual in nature, a lot can be done with the spells found in the good old Player's Handbook. All it takes is a little imagination to see a spell in a different light, and to use it to a new effect. It must be noted, however, that spells can be used to help as well to harm, and this carries over into the arena of sex. While magic can be used to make sex even more pleasant, it can also be used to make sex truly terrible. I'm willing to wager that most games will not delve into the worst that spells can do in the sexual arena. Torture, bondage, and other such things will probably be kept in the Underdark with the vile Drow. This is probably as it should be. However, in the interest of evil campaigns and/or terrible NPC villains, I will examine some harmful applications along with the beneficial:
Changing appearance: There are several spells that aim at changing a person's appearance (such as Alter Self, Change Self, and the Polymorph spells). These spells can be used to spice up a relationship by making partners look entirely different. They can also be used to prevent forbidden lovers from being recognized together; imagine how much easier it would have been if Romeo had been able to make himself look like a Capulet family member or servant! Spells that change appearance can also be used to trick people into believing that a person is someone they are not. This can lead to a person sleeping with someone that they normally would refuse and even worse confusion if pregnancy occurs. For the most part, only evil characters can stand to use alteration spells for sexual deception. Good or neutral characters who start to use such underhanded tactics should be considered on the expressway to evil.
Charm spells: Many of the charm-like spells in D&D can be used to get people to like you, and they might even do things for you if you suggest it. Some DMs will rule that it is an evil act to use any magic to make a target fall in love or be involved in sexual activity. Other DMs might rule that spells like Charm Person aren't bad enough to make a character slide into evil. Using a spell like Geas to force a target into romance is probably going to be considered an evil act by most DMs. Likewise, using Limited Wish or Wish to make someone fall in love could also be considered an evil act. While it might seem stupid for a wizard to use a powerful spell like Wish in the name of romance or sex, we must remember that some people will go to any lengths to obtain the object of their desire. Wizards are not immune to obsession. Clerics, on the other hand, can have a harder time using something like Miracle to make someone love them. Since they have to ask their gods for such a power, their request can always be denied - and some gods might be very upset that a cleric even tried to ask for such intervention.
Enhancing sexual encounters: Spells like Bull's Strength, Cat's Grace, and Eagle's Splendor raise the natural attributes of characters, making them stronger, more sinuous, and more attractive. These spells can be used to make sexual activity all the more exciting. Likewise, Enlarge can be put to some creative uses, especially if the DM rules that it can be used on particular regions of the body (instead of enlarging the whole creature). Fly and Levitate can make encounters particularly fun and versatile.
Creating the right setting: Spells like Dancing Lights, Faerie Fire, Ghost Sound, Mirage Arcana, and Prestidigitation can make the background of a tryst all the more romantic. On the other hand, Darkness can also make a sensual encounter more interesting by the very lack of sight. Regardless, if lovers can't find an inn or are far from civilization, they can use Leomund's Secure Shelter or Mordenkainen's Magnificent Mansion to provide comfort and privacy.
Message spells: There are several different spells in the PHB that can be used to send messages. Animal Messenger, Helping Hand, Magic Mouth, and Sending are only a few of them. Not all lovers can afford to be seen in public together, and to these folks messaging spells are very important. Some lovers will only be able to afford the simplest spells like Animal Messenger, but lovers will utilize higher level spells like Sending to ensure privacy.
Divination spells: It is not unheard of for people to use divination spells for romantic purposes. The greater divination spells like Commune are rarely if ever attempted for such purposes; the gods do not like their clerics to use such spells for trivial matters. Spells like Augury, however, are good for telling someone if they should risk meeting their lover at midnight or if a marriage proposal will go well. Detect Thoughts can give a character an idea if someone thinks favorably of them or is attracted to them.
Languages: Spells like Comprehend Languages and Tongues can allow characters to converse with cute foreigners and travelers.
Images: Spells like Silent Image, Permanent Image, and Persistent Image create likenesses of characters. Some of these images are only visual, but others also replicate sounds, smells, and other effects. Nothing says that such images have to be clothed, and it is up to the spellcaster to decide what images are doing. They could be used for the erotic entertainment of others quite easily. On a slightly sinister note, the spell Clone creates a replica of a person that has no soul. While the spell says that the replica is inert, that doesn't mean it couldn't be moved, posed, or otherwise put to use.
And now, for alternative implications:
Healing and Inflicting spells: If Inflict Wounds spells are being used as a means of sexual torture, then Cure spells will probably be necessary to keep the target alive. While these spells are not normally utilized in the sexual arena, they certainly can be.
Otherworldly companions: Spells like Gate and Planar Binding bring creatures from other planes to the Material realm. Some of the creatures (like celestials and demons/devils) are generally able to copulate with humanoids. Sometimes offspring can result. (This is how the Drow create Draegloths, which are Drow/Glabrezu hybrids.) Some creatures will be happy enough to perform sexually if they are called for such a purpose; others will have to be bargained with very carefully.
Voyeurism: Many spells can be used to look in on other people, regardless of where they are or what they are doing. Arcane Eye, Prying Eyes, Clairaudience/Clairvoyance, Invisibility, and Scrying can allow spying and voyeurism to take place. Discern Location can make it so that a character can be followed no matter where they are located.
Bondage: For those characters into bondage, magic exists to make the task of binding easier. Hold spells can make a target still, and Animate Rope can bind them nicely. Evard's Black Tentacles can be used to hold a target still, and can also be used for scenes reminiscent of hentai anime. If a target is kept in a room, Arcane Lock and some forms of Binding can help keep them there.
Softening targets: Spells like Mind Fog and Feeblemind can help to soften targets up and make them easier to control. Sleep grants a few minutes before the target wakes up. Using these spells to elicit sexual activity will probably be deemed evil acts by your DM.
Other "partners": For those into bestiality: Animal Friendship, Animal Growth, Animal Shapes, Dominate Animal, and Mount all apply. Or, for those druids or rangers very much into plants, spells like Awaken, Command Plants, and Control Plants will suffice. A few people might use Animate Object to create a mindless automaton for their pleasure. Far more vile, there are a rare few necromancers that will use spells like Gentle Repose and Animate Dead for their own twisted purposes.