Another theme might be subverting traditional storytelling. By favoring the villainess, it goes against the normal narrative where the heroines are always the 'good' ones. This can lead to exploring different moral and ethical concepts.
The protagonist who favors the villainess can also be quite interesting. Their reasons for siding with the villainess, whether it's because they see something special in her or they want to change the story's course, can add depth to the character.
A common trait is also being manipulative. The villainess will try to manipulate the situations and the people around her to get what she wants. She might manipulate the male leads by lying about the protagonist or creating misunderstandings between them to drive a wedge in their relationship.
Well, first, you could start by using specific search engines for fanfiction. Some of the more popular ones are dedicated to different fandoms. Also, check out relevant forums or communities where fans might share or recommend such fanfictions. Maybe there are some Tumblr blogs or Reddit threads that focus on this particular pairing and could lead you to the desired fanfiction about their kiss.
You can find rei x shinji fanfic on some popular fanfic websites such as Archive of Our Own (AO3). There are numerous stories there with different themes and interpretations of their relationship.
You can try some popular e - book platforms like Amazon Kindle, or check your local library's digital collection if they have a wide range of novels available. Sometimes, official websites of the publisher also provide options for reading.
To survive as a villainess in a deadly novel, you need to be smart. Try to figure out the key events and avoid getting involved in the dangerous ones. For instance, if you know there's a big battle coming up where the villainess is supposed to die, find an excuse to be elsewhere.
If I became a villainess in a deadly novel, I would first try to understand the plot and the reasons behind my character's villainous actions. Maybe I was misjudged or there were some misunderstandings. Then, I would attempt to change the course of the story. I could start by being kind to the protagonists and trying to form alliances with them instead of opposing them. This way, I might be able to avoid the 'deadly' end that was originally set for my character.