Fictional characters will always play into an idealization of some sorts and will mostly have at least one physical or character trait we find attractive or kinda cool at the very least. Even characters who are totally lame or hideous will have something to appeal to us.
I was hoping someone would bring this up. I agree, also, lets not forget how most fictional character, especially those that are meant to be attractive, are drawn with ideal proportions and physiques.
This is why all dudes have some musculature, and all girls have perfect bodies and faces. Even if they are stylized with a manga style, they still follow the ideal proportions and are meant to be seen as attractive.
This is why I can't diss on someone who is attracted to 2D girls, as I can understand it completely, and yeah, I've been there too.
I WILL however diss those who take it too far with the Daikiwhatever and the worshiping of fictional characters:
However, it does bring up an interesting question about the future. When human-like AI becomes a thing, I wonder how many people will forego real relationships. I'm sure it won't only be the neckbeards on 4chan.