This is the exploration of the character motivations of a succubus and a dryad, and how they might engage in, eventually, in erotic encounter(s).
While a lot of the following is borrowed from many sources, it does not always follow known understandings, or rules from role-playing games. I borrowed where I thought it worked, and threw out or changed what I did not want. For example, some source describe dryad's as having bark-like skin. I discarded this notion for my own reasons. I did however stay as close as I could to the generally held beliefs.
Dryad - A dryad is a faerie-like creature of the forest, and is especially associated with an oak tree. Her and the oak tree share a spiritual entity, although physically they are their own entities. They are beautiful elf-like females with all the same features of any humanoid female. While not completely naked, what they do wear is largely ornamental. Dryads are good creatures, resorting to violence only if their tree or surrounding forest are put at risk, yet is otherwise neutral when it comes to law and chaos outside of nature. A dryad may be old in human terms, but is not necessarily wise to anything beyond her immediate sphere of influence and would otherwise be considered naive. A dryad likely would possess similar emotions as other beings...curiosity, fear, excitement, etc. So long as her tree and forest are safe from harm, she would be free to explore whatever emotions that might be appropriate. Being a creature of nature however, anything she would or might do would remain in accordance with nature. Dryads do not not generally engage in combat but do have at their disposal a wood handled bone knife.
A dryad has three significant abilities. Once per day she can teleport from any tree to her oak tree and only with in the limits of her surroundings. She can speak to plants of any kind, and where appropriate hinder someones movements by manipulating the plants. She can easily blend into any foliage-like environment and not be easily seen.
Succubus - A succubus is at heart a demon. It's primary purpose is to tempt and seduce weaker beings for the purpose of delivering their souls to hell. It does this by taking the form of a comely woman. Its natural form is also that of a flawlessly beautiful woman, with demonic bat wings, small horns above its forehead and fangs. They are of above average intelligence and not unfamiliar with the material plane or world. Being a demon it operates only out of selfish pleasure or gain, and does not necessarily have a rigid agenda. Its motives could be unpredictable. Because its makeup is largely of a sexual nature, more often than not this would be its motivation for just about anything it does. Although a succubus is inherently evil, due to its intelligence it would not be unheard of a succubus setting aside evil intentions, if temporarily, to suit its needs. It is also just as cable, and willing to receive pleasure as to dole it out. It's style is aggressive, but measured to ultimately reach its goal. A succubus carries no weapon other than its sharp nails and teeth. While they can and will operate independently, they can also be under the influence of a more powerful demon or devil.
A succubus has three significant abilities. It can summon a globe of darkness around herself and her immediate vicinity for the period of one hour per day. It can drain a creature's energy rendering it weak and unable to defend itself, it does this using a kiss, it can do this once per day and lasts as long as the succubus is in contact with its victim. It can assume a normal human/elf form for the period of one hour once a day. A succubus can fly, if briefly and only short distances.
Plot - The idea is to explore under what conditions and circumstances these two creatures would indulge in an erotic encounter (in this case two female forms) and what that might be like. The writers would as best as able keep within the guidelines of the character's motivations and agenda, using their abilities to meet their goals or even hinder the other where appropriate.
How these two characters get to this point is open to conjecture, however this is how the initial story would roughly be started. The dryad would stray outside its forest drawn by some curiosity. The dryad would happen across the succubus, who initially would be unaware of its presence. The dryad would admire the terrible beauty of the succubus, perhaps even in the process of seducing and indulging itself with a 'pet'. The encounter would be brief however and soon the succubus would be aware of the spying dryad and the dryad would run off in fright. Both creatures would contemplate the unsettling encounter, and thereafter would begin the seduction and the possibility of an erotic coupling.
A succubus is a creature of opportunity and often takes the path of least resistance when it comes to its victims or prey. How then might a succubus be persuaded or decide to ensnare herself a wood nymph? They share similar features, and while one is a thing of evil and chaos, nature is not generally speaking lawful. As said, a succubus could easily have its own motivations, is intelligent and hardly a mindless drone.
Would a dryad be repulsed by a succubus, a demon, presuming she even knew what a demon was? Beauty can be found in the random flaws of nature. The wolf has terrible fangs, the bat has leathery wings. Might she mistake this creature for something of nature? A lonely guardian of her forest, might she long the touch of another, similar shaped being? She's hardly unfamiliar with the caress of a warm breeze on her face, or the cozy snuggles from a rabbit or fox.
Setting - The dryad's forest is her realm, and can quickly determine if any being sets foot in it by speaking to plants. Her forest consists of her mature oak tree, many other trees, bushes, undergrowth as well as mammals, and a stream. The succubus resides not far off in a mountainside cave where she would set out from to any nearby villages tempting and seducing weak mortals. Whatever implements of seduction or comfort she may possess is up for conjecture. While generally speaking lazy, it would be likely it would not be without creature-comforts.