Option A: Dodge and Duck. If confronted by someone, I'd say my account was hacked by Anthony Weiner. Then as we all had a good laugh, I'd ask if they had seen the movie Gravity yet and slowly get the subject changed until they forget why they came to me in the first place and withdraw back to hiding.
I'd just need to be careful for about 2 weeks maybe three. But that time, other things should have come up in people's lives to make them forget this or at least not care too much anymore. Meantime, while waiting it out, I'd do what I could to bury the evidence. So, if that means, liking a whole lot of stuff or creating misdirection of some sort for people, I'd be on it. If I could find something even more embarrassing that someone else had done, I'd link that and try to make my mistake look less severe.
Option B: Create some kind of article talking about all sorts of the dispicable stuff that Hentai porn engages in and how it needs to be fought and all that moral jazz. Maybe have a call to arms of how people need to speak out against it and see it criminalized or come off the web. After completeing this, I'd then state that I was liking this article and trying to get other people to join in the fight. The article is called what it is just to get people's attention and to highlight one of the many terrible things found in Hentai form.
Option C: Just state that I did it for laughs. I thought that people would find it funny but the reaction was totally not what I expected and thinking about it now, I can see why and it isn't as funny as it seemed to me at that time. Guess I needed more sleep and sorry for not thinking about it more.
Option D: Tell people I don't have a little sister and so I was wondering what my life would be like if I had had one. I just thought this was normal behaviour in families. I mean, people married their sisters in history. The bible mentions instances of it also. Plus, Clueless and The Royal Tenenbaums kind of had brother/sister romances although it was because one of the siblings was adopted. No one told me it was something really wrong before. (Sure, it might mean people think you are really stupid but it's better that than the perv you really are. Plus, mentioning that it happened in the Bible has a way of getting people to back off and or change the subject.)
Option E: Confront my sister (and her friends) and then see where it goes....