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.
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.
In the ending story, Nanami's growth as a kami is a significant event. She has proven herself capable. Also, the relationships between all the characters, not just Nanami and Tomoe, are solidified, bringing harmony to the story's world.
One popular trope is the 'reincarnation' trope. In these fanfictions, characters might be reincarnated in different time periods or under different circumstances, which often leads to new and interesting storylines. For example, the main character could be reincarnated as a different deity or a human with some sort of connection to the original story.
You can try websites like Fanfiction.net or Archive of Our Own (AO3). These platforms usually have a large collection of fanfictions for various series, including Kamisama Hajimemashita.
I really like the fanfic 'Tomoe and Nanami: Unspoken Promises'. It focuses on the more subtle moments between them. There are many sweet scenes where Tomoe shows his protectiveness over Nanami in his own unique way. It's a relatively short but very engaging read.
I think fanfics that involve time - travel in the 'Kamisama Hajimemashita' universe can be really exciting. For instance, if a character travels back in time to change an important event in the story. Also, those that explore the mythology and lore of the series in more depth through creative plots are worth reading. Some fanfics might even introduce new supernatural elements that fit well with the existing 'Kamisama Hajimemashita' world.
You can try some fanfiction websites like FanFiction.net or Archive of Our Own. They usually have a wide range of fanfics including those for 'Kamisama Hajimemashita'.
In the 'Kamisama Hajimemashita' full story, the key characters are Nanami, a girl who becomes a god, and Tomoe, a fox spirit. There are also other important characters like Mizuki, another spirit who has a certain connection with Nanami. But Nanami and Tomoe are the central ones as their relationship drives much of the story. Nanami's journey as a god and Tomoe's changing feelings towards her are important aspects of the plot.