well I am in 2 minds really. I can understand you being turned on by her sexy body, that is a natural thing and especially if you have seen a live female pussy, well that would get any guy hot.

But as to going further with it, well there is the dilemma. Sibling sex is not taboo for no good reason as there is a higher than usual chance of problems with any offspring resulting.

I would find out how your sister feels about it all first, she may not appreciate you jumping in the shower and fucking her at all.

If you are excited and force her that is rape. Do you love your sister, would you want her to be raped? worse still if it is a family member, man that sort of thing could wreck you, your sister and your family forever, thats too high a price to pay for a fuck.

So talk to your sister and tell her how you have a crush on her and have the hots. Work out what happens from then from her response.

On no account jump in the shower with her uninvited.