First of all, yes Japanese like their heroes to be feminine men or masculine women. Men without so much testosterone are much better at emanating that oh-so-important "cool" image in Japan. We prefer macho guys like Bruce Willis who jumps from buildings and figures out things as he goes, while in Japan the more refined style, the man who keeps a cool head and has all the answers already is more popular. This often (but not necessarily) coincides with a more feminine style too, which would make typical westeners go "gaaaay", but then the Japanese have a much more relaxed attitude to this kind of thing anyway. Bishonen represent good-looking, clever (unless it's hyper-bishonen) and cool, which is something we all wish we could be, no? The gay stuff is just an interesting side-effect, imo. Now, the actual reply:
And about Sephiroth and AC. He's proven his feminity in one, very strong way - the end of trailer sentence "watashi wa omoide ni wa naranai sa". When a man is using "watashi" it already is a 'subtle' hint on him, and "sa" as well (though it can also imply feminity and sub of the person he is talking to). What EmperorSteele said about men-view-in-Japan is true. The more feminine the better a hero will be. For Japanese for everone to have a pinch of homosexuality is the perfect resolution, contrary Europeans which have a thing against that..
Actually, "watashi" is relatively gender neutral. While "boku" and "ore" are more exclusively used by men, "watashi" is frequently used among both genders. Among men it is often used when you want a more refined or polite level of speech than the casual "boku" or the impolite "ore". It is only feminine in the sense that it is less masculine.
The "sa" pattern is also used among both genders, although in slightly varying situations. There's the slang sound of just adding "sa" throughout your sentences to serve as small pauses (like "ano", "eto", "ga", "kedo" etc. can be used), and there's the more grammatical use, where "sa" is similar in meaning to "yo"; it adds a sense of sureness, personal conviction or explanation/reason. In this sense, as spoken by Sephiroth, "sa" is in fact a bit masculine and used more frequently among men than women.
That having been said, "sa" isn't particularly masculine and there are certainly lots of more "raw" wordings you can use to express your manliness. Doing so often lowers the class of the speech though, and I suspect this is the primary reason Sephiroth speaks the way he does. He's a madman, but he's not a stupid madman. He's a psychopath who thinks himself better than the world, he's clearly not going to speak like some testosterone-crazed teenager. He's more refined than that, and his speech reflects that as being less raw/masculine.
In closing, I wouldn't call his one line so far in AC a proof of his femininity. He's got the bishonen
look (which is why he's so popular in shonen-ai), but he's clearly not the type to groom his eyebrows when he wakes up in the morning.
If he's feminine, it's more because of the rather striking contrast to our western muscle-pumped characters of macho manliness. Just my two yen of course, I'm just saying that by Japanese bishonen standards he's still quite macho.
(the official Sephiroth that is, fan versions of him tend to ...use artistic license. Ooh boy. ~_~ )In second closing, it's amazing what a long analysis I managed to make from that one sentence he speaks... I haven't even played the Japanese version of FF7 to see his speech patterns there. ^_^;