In the lemon fanfiction about Natsuki and Shizuru, the focus might be on their interactions. It could be that the writer wants to show their chemistry in a more intense way. Maybe they are given more romantic or tense moments together, which can make the readers see their bond from a different perspective.
Another common theme is loyalty. They are both loyal to each other in the original, and fanfics build on that, showing how their loyalty can be a foundation for a closer relationship. For example, in many fanfics, they stand by each other in difficult situations that test their bond.
One common theme is friendship. Since they are friends in the original work, fanfictions often explore the depth and different aspects of their friendship. Another theme is growth. They both grow as characters and how they influence each other's growth is often a part of these stories.
Friendship is a very common theme. Their relationship starts as a friendship in the original work, and in fanfiction, it often gets explored more deeply, like how it withstands various difficulties.
Another theme could be the development of their relationship in a more adult - like context, not necessarily in a sexual way, but in terms of more mature emotional exchanges and decision - making. For example, they might have to deal with complex family or social issues together that test their relationship.
In non - lemon fanfics, Shizuru is often depicted as a strong and composed character. She may show her loyalty towards Natsuki through her actions, like protecting her. Natsuki, on the other hand, can be portrayed as more impulsive but with a kind heart. Their relationship is usually centered around mutual understanding and support, with a deep emotional connection that is developed through shared experiences.
There are also fanfictions that focus on their backstories. For example, exploring their past experiences and how those have shaped them into the characters we know. This can add more depth to their relationship in the fanfiction. And of course, there are alternate universe fanfictions where they might be in different settings like a modern high - school AU or a fantasy world AU.
You can try fanfiction websites like Archive of Our Own (AO3). It has a large collection of fanfictions from various fandoms, and there's a good chance you'll find Shizuru and Natsuki fanfictions there. Another option could be FanFiction.net, though AO3 is often more inclusive and has better tagging systems for easier searching.
I'm not really aware of any popular Shizuru and Natsuki rated M fanfics. It might be a relatively niche area within the fanfic world for this particular pairing at that rating.