Rape stories I believe deserve special attention. There is nothing like a good rape story. I have a special affinity for them and I think they can have an impact unlike any another story. Love is displayed in it's clearest and most powerful in times of need and hurt. We've all jumped to the defense of a friend or family member, and this is when we reveal just how much we think of them. This is what occurs in stories of sexual assualt.

Willow and Oz are a great couple for a rape story, because there is quite obviously so much love there. Willow can appear as a very vunerable character at times, and it is quite possible she could be the target of an attack. Oz's most memorable moment is when Willow is in danger, when he smashes the pot in Choices. Oz too, is a vunerable, small man and who is to say that the rape victim is a female, or indeed Willow.

The Act

Rape is very symbolic. It is the single most feared and hated crime in our society. People fear rape more than they do murder. Rape is the taking of something that should only ever be given. Rape is the loss of many things; for the young it is the possible loss of virginity and/or innocence, for people of any age it is the loss of control and trust. This could have a huge impact on those around the victim too. A fab rape story archived here is Helplessness and Healing by Leigh, in which Oz becomes angry at the rapist and has clearly lost all trust in that man, resolved to track him down.
The ripping of clothes is a very symbolic element of assualt and appears in many fics. It could mean the destruction of the victim/family's life, trust, and innocence. Of course removal of clothes is necessary for rape to occur, but don't underestimate the power and possiblity a torn piece of clothing and the effect it can have upon a story or character within it.
Obviously I'm assuming here, as in most stories in the fandom, that Willow is the victim. This can bring out so much from Oz. The protective side of his nature will be revealed. Common feelings are those of anger, helplessness, and more often than not, guilt. I will bet you anything that Oz would feel very guilty that he did not protect Willow or somehow prevent this from happening. What if the rapist were someone close to Oz and/or Willow. This would heighten any emotions and prove as a great shock to the characters. You, as a fanfic writer have a certain power over the reader, and there is nothing to say you must reveal the attacker initally or even at all. Leigh cleverly doesn't disclose the attacker until late into the story, even leading us up the garden path at one point. The victim may even be Oz, or another male. A man will quite often feel weak to have let this happen, and is less likely to tell anyone about the incident. Fanfic authors bear that in mind.

The Aftermath

The intial feeling is bound to be one of shock, anger and need for revenge, only after the victim has been ensured of safety. Check out H&H for more on this. The aftermath is an emotion. Fics tend to focus on the victim (Willow), and the other half, or closest person, (Oz). But this can effect anyone, so if writing a fic, be sure to voice the views of those around.
Buffy for example is an interesting one. Willow is her best friend, not only will she think she has failed Willow as a friend, but also as the slayer. Buffy has protected Willow and the rest of the world from vampires, demons and certain doom, but couldn't stop thishappening to her friend at the hands of a human being. Why couldn't she? How is this going to make her feel? Exploration of this makes for a great story and superb characterisation.

Whatever you do, do not attempt to cure sexual hurt with sexual comfort, not unless you are truly sure this is the right thing. Believe me, I've seen this in so many stories and it is hideously inappropriate.

Good luck, with whatever you do, in any fandom. I humbly suggest you give H&H a darn good read.