One idea could be that characters from 'kamisama no inai nichiyoubi' cross over into a different magical world. They might have to adapt to new rules and powers while trying to find a way back home. For example, the main character could meet new allies who help them understand the strange new environment.
The 'kamisama no inai nichiyoubi light novel' might revolve around the idea of how the absence of a god impacts the events that occur on Sundays. It could have various characters dealing with this strange situation, perhaps having to find new ways to solve problems or face challenges that were previously dealt with by the divine on Sundays. There may be elements of adventure, self - discovery, and exploring the implications of a god - less Sunday.
The main character from 'kamisama no inai nichiyoubi' would be very interesting as they already have a well - developed personality and backstory. Their reactions to a new crossover world would be a great focus. For example, how they handle meeting new and different types of characters.
I'm not sure exactly as I haven't read it fully. But usually in such light novels, there would be a protagonist who is likely to be deeply involved in the situation of the god - less Sunday.
A crossover with 'Fruits Basket' could also be cool. Nanami could end up in the Sohma family's world and befriend Tohru. Tomoe might be a bit jealous at first, but then he gets to know the Sohmas and they all work together. Maybe there's a curse involved that Nanami and Tomoe try to help break with the Sohmas' unique situation.
In a crossover with 'Naruto', Naruto himself would be a great addition. His positive and determined attitude could contrast with Tomoe's more reserved nature. And his powerful ninja skills could come in handy when facing some of the demons in the Kamisama Kiss world. Sakura could also be there, and she might bond with Nanami over their strong wills.
One possible scenario in such a fanfiction could be Nanami and Tomoe going on a journey to the spirit world together. They might face various challenges there, like dealing with mischievous spirits. Tomoe, with his powerful yokai abilities, would protect Nanami throughout the adventure. And Nanami, with her kind heart, could end up making friends with some of the spirits they encounter.
In a Tomoe x Nanami fanfiction, it would be interesting to write about a situation where they have to pretend to be a married couple for some spirit - world related reason. They would have to deal with all the implications of that, like sharing living quarters and acting affectionate in public. This would force them to confront their true feelings for each other.
There might be some fanfiction on FanFiction.net as well. However, the quality can vary greatly. Look for stories with high ratings and reviews. Some authors are really good at exploring the concept of Nanami being pregnant in the context of the Kamisama Kiss universe, adding new plotlines and character developments.
A possible fanfiction plot could be Nanami accidentally loses her powers and Tomoe has to protect her while also trying to find a way to restore her powers. In the process, they discover new things about each other and their feelings grow stronger. It could be a story full of action, a bit of angst, and a lot of tender moments.