Well, perhaps the kiss is part of a dream sequence at first. Iris dreams of kissing Nathaniel, and then later in the story, it actually happens in real life, which would be a really cool way to build up the tension and anticipation. This could also show how her subconscious has been thinking about him in a romantic way.
I haven't actually read a specific fanfiction about their kiss, but it could be really interesting. Maybe in the fanfiction, their kiss is a turning point in their relationship. It could be a moment of realization for both of them, where they finally understand their true feelings for each other.
Perhaps they could have a gender reveal party. Their friends and family gather around, excited to find out if it's a boy or a girl. There could be some fun moments like when the balloon pops and the pink or blue confetti flies out. After that, they might start thinking about baby names. Nathaniel could suggest some family names while Iris has her own unique ideas.
Well, in a fanfiction about Iris and Nathaniel being pregnant, it could start with a mysterious illness that Iris has. She goes to the doctor and discovers she's pregnant. Nathaniel is initially in disbelief. He has to quickly adjust his mindset from being carefree to being responsible. They could then go on a journey to prepare for the baby, like shopping for baby clothes and setting up a nursery. Their friends could be either very helpful or add some comical chaos to the situation.
The kiss could be the catalyst for them to start traveling together more often. They would share more adventures, protect each other during battles, and their relationship would grow stronger. Along the way, they might face some challenges from other characters who are jealous or don't approve of their relationship, but they would overcome those together.
Well, they might start to explore their relationship more deeply. Maybe Naruto would become more protective of Hinata, and Hinata would be more confident in their bond. They could go on dates and face challenges together as a couple.
A plot might involve one of them being in a relationship with someone else at first. But as they spend more time together, they start to develop feelings for each other. Eventually, these feelings lead to a passionate kiss. For example, Iris could be dating Barry, but then she discovers a deeper connection with Caitlin.
In a fanfic about Ash and Iris betrayal, perhaps Iris could betray Ash over a powerful Pokémon they both encounter. Maybe she feels that Ash is not strong enough to handle it and decides to take it for herself, thinking it will help her on her journey to become a top Pokémon trainer.
Well, perhaps they've been through some difficult times apart. Letty might have been in some sort of trouble, and Dom comes to her rescue. As he pulls her out of danger, their eyes meet. There's this unspoken connection, and they start to remember all the good times they had together. That's when the air between them gets charged, and it's leading up to that first kiss.
Maybe the kiss is a part of a mind - control scheme by Poison Ivy. She kisses Robin to make him do her bidding, like stealing something from Batman or leading the other heroes astray. However, Robin's strong will could start to break the control as he realizes what's happening and then there would be a struggle between his loyalty to the good side and the influence of Poison Ivy's kiss.
In a Bulma and Vegeta first kiss fanfiction, it could be a very intense moment. Maybe it happens after a big battle when they both realize their deep feelings for each other. Vegeta, who is usually so tough and stoic, might let his guard down and initiate the kiss, surprising Bulma. This could be a turning point in their relationship, leading to more emotional exchanges and a deeper bond.