The ending of 'Kiss Him Not Me' manga ties up most of the storylines neatly. The main character finds love and resolution in a way that's satisfying for fans.
Since I'm not familiar with 'kiss him no me light novel', it could potentially be a story centered around a female protagonist who is conflicted about her feelings towards a male character, which is represented by the 'kiss him no me' concept. Maybe it delves into her internal struggle between her emotions and her self - restraint.
As mentioned before, 'lemon' content is inappropriate, so I can't really discuss the characteristics in that regard. But in general 'kiss him not me' fanfiction, it often focuses on the romantic relationships between the characters, exploring different scenarios and emotions within the context of the anime's story and characters.
A 5x7 fanfiction for 'kiss him not me' might focus on a particular moment. For example, a 5x7 photo that holds a special memory for the characters. It could be a photo of a group outing, and in the fanfiction, the details of that day are explored, how the relationships between the characters developed based on that one moment captured in the 5x7 photo.