Does the title sound negative to you?
Before we start the discussion, I think we must make it clear first that antagonists meant in the title are not always love rivals, for shoujo/josei cases. Indeed most antagonists are related to the romance of the lead characters. Antagonists themselves can be defined as those who have goals or purposes opposing the leading characters. Feel free to clarify this if you think the definition is not accurate. :P
With that being said, let's start! Who do you think are the greatest, or most memorable, antagonists from shoujo and josei series you have read? Their greatness can be shown in many way. Be it their methods, or their words, or their attitude... Everything about them.
I would have to say... my Favorite character from a certain manga happens to be the "antagonist" of the story: Takumi from NANA (which you, P-chan, don't read so READ IT ALREADY )
Antagonists are often made to be cool so they can pull off a certain evil aura. I love Takumi's quirks though, and that's what sets him apart. Since he has very few cute moments but when he is portrayed in those cute moments OMG i could just eat him up
Vampire Knight is ridden with all sorts of antagonists. It's like... Yuki against everybody!
I believe well-written antagonists really do make you feel a certain frustration, make you wanna strangle them or pull their hair. The ones that fit this bill for me are those b*tches in sheep's clothing. Especially the lolita types! Gawd! The cutesy or elegant girl/boy that turns out to have ulterior motives. In shoujo especially, if a new cute girl is introduced and everybody likes her, put your money on it that she'll do something really evil!
It looks like I still have tons of series I need to check...
Either way, speaking of antagonists, I think we can consider Shou from Skip Beat! as such character? In the beginning he looks like a total jerk, really, acting so mean towards his number one fan, the poor girl Kyouko, not only with cold attitude around her but also with harsh words. Even after the story advanced we would still see how he tried to send troubles towards Kyouko in her path along the way. We got to see another side of him though in the next few chapters... how much I turn to love Shou after that, even though those evil ideas inside his head never gone away. XD