In this fanfiction, it could start with Annie realizing she is pregnant. Armin is overjoyed but also worried about the future. They embark on a journey to discover more about Annie's pregnancy and what it means for their future. Along the way, they learn more about each other and their relationship deepens as they prepare for the arrival of their baby.
Eren might be shocked at first. He has always seen Annie and Armin as comrades, and this sudden pregnancy news would be quite unexpected for him. He might be a bit hesitant but eventually come around to support them.
One popular trope is the 'enemies to lovers' dynamic. Given their positions as former enemies in the main story, it's common for fanfictions to explore how they transition from hostility to love. Another trope is the 'hurt/comfort' where, for example, Annie might be injured or in distress, and Armin is there to comfort her, which deepens their bond.
One common theme is the exploration of their relationship in a post - war scenario. How they deal with the traumas of the past and build a future together.
One common theme is the exploration of their relationship post - the main events in Attack on Titan. For example, how they reconcile their differences after all the battles. Another is the idea of them growing closer during training sessions that were not fully shown in the original series.
One possible scenario could be that in the fanfiction, Armin and Annie's pregnancy is a result of their deepening relationship post - the end of the main story's conflicts. Maybe they find peace together and start a family. Their different personalities, Armin's intelligence and Annie's stoicism, could create interesting dynamics during the pregnancy, like how they handle the news, their preparations for the baby.
Love and acceptance are also big themes. They come from different backgrounds and have different personalities. So, their journey to accept each other and fall in love is often explored. A lot of fanfics show how they break down the barriers between them to be together.
You can try searching on fanfiction websites like Archive of Our Own (AO3). There are a lot of works there. Just type 'Armin x Annie' in the search bar and you'll get a bunch of results.
To develop their relationship realistically, start with them having small interactions based on mutual interests or goals. For example, if they are both interested in understanding the history of the Titans, they could start by sharing research. Then, gradually introduce moments of vulnerability. Maybe Armin opens up about his insecurities regarding his intelligence not always being enough, and Annie shares her own fears about her past actions. This would create a deeper bond.
One plot idea could be that Armin and Annie are forced to work together on a secret mission in a post - apocalyptic world. As they face various challenges, they start to see each other in a new light and develop feelings. Another idea is that they meet in an alternate universe where their roles are reversed. Annie is the shy, bookish type and Armin is the tough fighter. They are drawn to each other's differences. And a third plot could be that they are both part of a resistance group against an oppressive regime. Through their shared struggles and sacrifices, their relationship blossoms.