Lets run through some scenarios, shall we?
Scenario 1. We have just started watching K-On. We meet our four girls. We are introduced to Ritsu. We find out that she is a person who recently broke up with her past boyfriend. Throughout the show, we see her coming to terms with the breakup and finding a new love (possibly a new yuri love?!) and by the end, this love has made her find happiness. The fanbase spends the whole series pissed at her old boyfriend, cheering her on, and full of joy when her heart is filled again. This all plays sub-story to the main show, sort of like Konata’s story in Lucky Star, but it gets itself some great jokes and touching moments to go with it.
Scenario 2. It’s episode 6 or 7 in the series, and we find out that there is a shocking truth behind Yui’s retardation. As it turns out, she was sexually abused at one point in her life, and the shock from back then made her go a little kooky. She used to actually be very intelligent, but lost a lot of it in the incident which was buried deep inside of her. Through her experience in the series, she starts to gain back her intelligence and overcomes her past. When the revelation is made, the fans get even more deeply in love and connected with Yui and want to protect her and make her happy and bring her back from that trauma. This leads to infinite touching moments and tears being shed, plus people who hated Yui for being such an idiot get their reasoning and justification for her stupidity and are able to stop hating her as much.
Scenario 3. Once again, it’s episode 6-7. We find out that Mio actually had a boyfriend some time ago before joining the K-On. They were pretty serious at the time, too, so there is a chance that they could have had a sexual encounter. The relationship ended on bad terms, so Mio doesn’t like to talk about it. The fans become furious. Many drop the show, burn the manga, vandalize the Kyoto Animation offices, and demand their time and money back for ever bothering with the show.
Well, that last one ended in disaster. But why? Seems like the things she went through were no different than the other two characters. But it’s all a matter of timing and consentuality (not a word). In electronics terms, it’s like a NAND gate. The truth table would look like:
Now, lets support these theories with some examples.
1. When a character is introduced as having a sexual background, it lessens, if not fully erases, the blow of them not being a virgin because it is something we know from the beginning. Obviously, a lack of virginity without a lack of consent is not enough to make a character hated. Mom characters, even if they are single by divorce, are always hugely popular. We have characters like Misato from Evangelion who we know has had sex before as a mature woman with a hell of a slutty side, who are still popular. It isn’t because they are older, it’s just because we knew from the beginning that this was an aspect of their character. We can start right off with this person in mind as a non-virgin and cheer her on in her endeavors and love her for reasons that have nothing to do with her purity.
2. Rape always works as a plot device. Always. Especially in moe anime. It can be something we know from the beginning – see Bitter Virgin (which is shoujo but has a large male fanbase who are the moe type) or Elfen Lied. In this case, we root for the character from the beginning because she is broken and we have this sense of needing to fix her, and we may feel that her purity was stolen from her, rather than that she lost it. It may even turn around and make her even more pure in our hearts than before because her innocence was taken advantage of. As a dramatically timed revelation, it can have an even huger effect like in ef ~a tale of melodies~. A character who was already endeared for other reasons now has this endearment super collided with that of being a raped character. The love and sympathy may create one of the ultimate forms of moe. This can also work by the rape even happening on-screen, as it does seem to happen in fucktons of eroge (pissing No Name and I off to NO END.)
3. The problem arises when we learn that a character is not so pure, doesn’t mind it, and didn’t tell us. A character who acts as pure and innocent as any other is suddenly revealed to be less innocent and unworldly and actually may have had sex in the past with someone else. To many otaku, this is like betrayal for a woman to act innocent and fulfill their fantasies, only to turn around and not actually be innocent. It’s kind of like a girl flirting with you and going on date-y things and only telling you later that they have a boyfriend, just because you didn’t ask (this happened to my brother, though he impressively hung in there anyway.) It sucks, and you feel like she may have been fake all along and not who you thought she was since she’s been keeping things from you.
(EDIT: No Name reminded me of another great example: Shugo Chara. One of the main female characters turns out to be a man after 38 EPISODES. It was enough for both of us to drop the show for over a year, and he still hasn’t picked it back up since, well, ‘he fapped to it’. This is exactly what I mean.)
Sex is treated as a pretty big deal in storytelling. It, more than anything, seperates the mature stories from the lesser-mature ones, and creates depth in characters by it’s mere existence. Especially in anime, it’s one of the biggest character traits – after all the important moments in an eroge are the ones that get you into bed with your girl. Relationships are most defined by whether or not those involved are fucking or not. What we know about a character’s sexual experience is one of their biggest defining characteristics, even if that experience is none, and adverse reactions can be expected.