Fael is a strong, experienced young elven warrior. Even at her young age she has done melee combat against countless foes, and proven herself a capable warrior. As such, she is one of many elves assigned to patrol the Great Forest. They make sure nature doesn't get disturbed, and no hostile force goes in. She is ordered to bring any intruder in as a prisoner to be questioned by the elves.
Today, Fael is patrolling an unknown area of the forest, when she spots an intruder, a human who ventured too far into elven territory. The human is alone and seems no match for the elf warrior. She quickly confronts him and takes him prisoner, before starting the long walk back towards her village. However, the human has a hidden advantage. He knows that berries growing in this part of the forest have a unique property. They arouse anyone who eat them. As soon as someone ingests a few berries, they start getting an irresistible urge for sex. Fael doesn't know that, and the human decides to try and get lucky, and perhaps even get his freedom. There's no way he can confront the elf warrior, so instead he convinces her that they should stop to rest and eat some.
When she eats the berries, the effect is very quick. As they resume their walk, she starts getting aroused, and begins to touch herself, her body highly turned on, until she has no choice but to start removing one piece of armor at a time, caressing herself madly, until she's completely naked, and accepts her prisoner's offer to have sex, so she could have release.
For this story I'm thinking we could start when your character, a male or female human, gets captured, and then they would convince Fael to eat the berries in order to get her naked and to have sex. It could even go further, where she doesn't realize that it's the berries that did this and he makes her eat more and she starts going crazy being so aroused, and he/she slowly becomes her only avenue of relieving herself. We can take this as far as you want, I'm open to extremes if that's something you wish.