A theme that often comes up is his physical pain and how he endures it. This can be used to show his strength and tenacity. For example, in a battle - themed fanfiction, he endures great pain but still manages to fight for the sake of his village. Also, the theme of self - discovery through pain is common. As he experiences pain, he learns more about himself and his limits.
The theme of sacrifice could also be present. Both characters are willing to sacrifice for their causes. In the context of a yaoi fanfiction, this could translate into sacrifices for each other. For example, Pain might sacrifice his original plans for world domination for Kakashi, or Kakashi might put his village - related duties on hold to be with Pain, exploring the lengths they would go for their relationship.
Another possible fanfiction could be centered around Kakashi's pain from his past traumas, like the loss of his father. It could show how these past experiences resurface when he faces a new threat in the village. The story could detail how he overcomes this pain by finally coming to terms with his past and using it as a source of strength.
This type of fanfiction is very controversial. Naruto represents hope and growth in the series. Kakashi, as his teacher, is supposed to guide and protect him. Having Kakashi kill Naruto would completely disrupt the established character arcs and the overall positive message of the 'Naruto' story. It might only appeal to a very small subset of fans who are interested in exploring extremely dark and alternative scenarios.
I'm sorry, I don't have specific 'Pain x Kakashi' yaoi fanfiction to recommend directly. You can try searching on fanfiction - specific websites like Archive of Our Own (AO3). They usually have a wide variety of fan - created works including yaoi pairings.
In some fanfictions, there could be an alternate reality or a time - travel plot involved. Maybe Kakashi from the future accidentally goes back in time and in the chaos of trying to fix something, he ends up killing Naruto. This would completely change the course of the Naruto - verse. Characters like Hinata, who had feelings for Naruto, would be heartbroken. And the Akatsuki might take advantage of the situation, seeing the Hidden Leaf Village in a state of disarray without Naruto as their potential Jinchuriki and future hope.
It's rather unique. In the original Naruto story, Kakashi is a mentor to Sasuke, and their relationship is complex but not one typically leading to Kakashi killing Sasuke. So in fanfiction, this would be a very out - of - the - ordinary plot that goes against the general character dynamics we know.
The reason why doctor novels wrote about fighting and killing was probably because the creators wanted to show the professional pressure and risks of doctors and the challenges and difficulties that doctors had to face when dealing with emergencies. The field of medicine and biology involved many complex biological and chemical processes that often required extreme methods to solve. Doctors often need to take some high-risk measures in surgery, diagnosis, treatment, etc. Therefore, showing the working environment and work content of doctors in the novel can help readers better understand and feel the uniqueness of the doctor's profession.
Indiscriminately killing the innocent meant the same thing. They both referred to killing innocent people. Killing the innocent meant killing innocent people, and killing the innocent meant killing innocent people. Therefore, killing the innocent and killing the innocent could be used interchanged to express the same meaning.
Fight was a movie released in 1981 and directed by Li Zuonan. The movie was an action movie, and it gathered Xu Shaoqiang, Chen Huimin, Wang Guanxiong, Nagano Juhua, Wang Dao, Gao Fei, Tong Lin, Liu Yali, and many other capable actors. The film was released in China Taiwan and was 98 minutes long. Other than that, other information about the movie could not be confirmed for the time being.