Love and relationships could be part of it too. It might not necessarily be romantic love, but the love between friends or family - like relationships. For example, they could be helping each other through heartbreaks or celebrating joys together. And sometimes, in the fanfiction, they might be part of a community where the theme of unity and cooperation is emphasized, working together with other characters to achieve a common goal.
I'm not sure about specific izzy and mimi lemon fanfiction, but you can try searching on fanfiction websites like Archive of Our Own. There might be a variety of stories there that could interest you.
Adventure is also quite common. They might go on a journey, either physical like a trip to a new place, or metaphorical like trying out a new hobby together. This allows for the development of their characters and their relationship. For example, they could be exploring an old, abandoned house in one fanfiction and in the process learn more about each other's fears and strengths.
One common theme is friendship exploration. The kiss could be a moment of intense friendship or a realization of a deeper bond between them.
One common theme is adventure. Since they are often associated with a world of pirates and exploration, the kiss might happen after they survive a dangerous adventure together. Another theme could be friendship turning into love. Their existing friendship blossoms into something more romantic, leading to the kiss.
One common theme is the idea of 'opposites attract'. Maybe Jake is really outgoing and Izzy is more introverted. But they find that they complement each other perfectly. Another theme could be 'forbidden love'. There might be some external factor like social status differences that they have to overcome.
Growth and self - discovery are themes as well. In the context of their relationship, both Joe and Mimi may grow as individuals. They might learn more about themselves, their desires, and their future through their interactions with each other.
Another theme could be self - discovery. As they interact with each other in the fanfiction, they learn more about themselves. For example, Davis might discover a more confident side of himself because of Mimi's belief in him. Mimi, on the other hand, could discover her more adventurous side with Davis by her side. This theme often makes the characters more relatable and the story more engaging.
One common theme is the adjustment to married life. How they handle daily routines, share responsibilities, and deal with small arguments that come up. For example, in some fanfictions, Tai might be shown as forgetting to take out the trash, and Mimi gets a bit annoyed, but they work it out in a cute and humorous way.
Adventure is likely to be a theme. Their unique personalities could lead them into all sorts of exciting situations in fanfic, like exploring a mysterious place or solving a strange mystery.
One common theme could be the encounter between the demogorgon and the characters in a more 'lemony' or romanticized (in a very strange way) context. Another might be the exploration of the demogorgon's nature within this fictional and often out - of - the - ordinary relationship - type situation.