One of the main themes is adventure. Since rengoku is often involved in battles and dangerous situations, the fanfics may take the reader along on these adventures. They might face demons together and their relationship develops through these shared experiences. Also, loyalty is a big theme. Rengoku is a very loyal character, and this loyalty extends to his relationship with the reader in the fanfics.
Well, some popular rengoku x reader fanfics can be found on Wattpad as well. Look for ones with high ratings and good reviews. They usually offer different storylines, from adventure - filled ones where rengoku and the reader go on quests together, to more romantic and heart - warming stories about their relationship.
As of the current manga chapters, Sanemi is still alive. His character has gone through many challenges but has managed to survive. The plot continues to unfold with him as an important part.
One common theme is adventure. Since both characters are from the Demon Slayer universe, they often go on demon - slaying adventures together in the fanfictions. They might face powerful demons and rely on each other's skills to survive.
Since I don't have specific details about this 'sanemi light novel', it's hard to say precisely. However, in many light novels, the plot often includes elements such as a unique setting, be it a fantasy world or a post - apocalyptic one. Sanemi might be at the center of a mystery or a power struggle. There could be a love interest involved too, which could add an extra layer of complexity to the story.