"Willow?" she calls. Is she addressing you? You have a feeling she is, so you regretfully push your way out of your tree to see what she wants. "Are you calling me?" you ask.
She nods. "I came to see how you were feeling," she smiles.
You sigh. "Um...confused, really. What's going on here?"
She laughs. "Isn't it clear? You've become a dryad."
"I know that," you groan, "but why? What did I do to provoke you?"
The fairy giggles. "Oh, you didn't think this was a punishment, did you? The forest just needed a new guardian for its willows, and you answered its call, though you didn't know it at the time."
You are surprised. "Its...call?" you ask. She nods again. "The forest called you here to guard the willows, and we were the ones that made the change so that you could. You did cause a little damage to our ring when you arrived, but this wasn't something punitive. You're here because you need to be, and you're a dryad because you need to be. That's all there is to it."
"B-but," you sputter, "I'm not a dryad, and I'm certainly not female! I'm supposed be a guy! A human guy!"
The fairy giggles again. "Oh, Willow!" she laughs. "That all changed when you answered the call, don't you know that? You are exactly what you're supposed to be, silly girl!"
You are taken aback. "W-what do you mean?" you ask.
She laughs some more. "You've been changed, Willow, dear," she smiles. "When you're changed by a fairy, whatever you were before doesn't matter anymore. You don't just have the body of a dryad, you are a dryad. If you were still a human inside, why would you be so perfectly at ease without clothes on?"
You want to blush as you realize that she's right and you are in fact unclothed, but somehow you can't seem to make yourself feel bad. Being naked isn't a taboo for you anymore; it's just how you are, no sexual implications attached. "You see?" the fairy laughs. "You don't need clothing because you're a dryad. And similarily, you'll find that, after the initial shock, you're perfectly at ease with being a girl. That's just the way fairy changes work."
"W-what," you begin, pausing to sort through all the questions in your head. "What am I supposed to do?" you finally ask.
"You guard the willows, of course!" she snorts. "Goodness, girl, did no one ever teach you about dryads?"
"Not much," you mutter, a little embarassed at your general lack of knowledge on the subject. The fairy smiles and strikes a "lecture" pose.
"You're here because the forest called you," she says. "Specifically, you were called here to protect the willows, since the previous guardian died. That means you have to take care of all the willows in the forest. If they're not getting enough water, make arrangements with the naiads to move a stream. If they're sick, you have the power to combat their disease. You can let some of them be cut down if you must, since humans need wood sometimes, but don't let too many of them be damaged. That shouldn't be much of a problem anyway, because willows aren't good lumber trees, I don't think. As for you, as long as there's a willow left in the forest, you won't age. The willows are all your trees, like the one you were just in. You can go inside them and stay as long as you like, like you did earlier. But remember, although you won't age, you can still be killed if you're not careful. None of the creatures in the forest will harm you, but if you get seriously injured, or if all of the willows die, you'll die. Beyond that, if your trees are all healthy, you can just enjoy life! Bond with your trees like you were earlier, or come out and interact with the other spirits of the forest, or just come out and spend some time by yourself!"
"But I...I..." Words fail you. This can't be right, can it? And yet somehow you sense that she's right. Your place is here, with the willows. There are other spirits in the forest, the fairies, the naiads, and the other dryads, for you to be with if you need company. A warm feeling fills your heart; the fairy is right, the forest is your home now.