Well, one theme could be the exploration of new identities. Ulquiorra and Orihime would have to redefine themselves as they are about to become parents. There could also be a theme of community support. How do their friends and the people around them react to the news? Do they offer help and guidance? And a theme of sacrifice might be involved too. They may have to sacrifice some of their own desires and freedoms to take care of the baby and build a family.
The theme of hope is very possible. In a world where they've faced so many difficulties, the pregnancy could be seen as a sign of a better future. It might also have a theme of growth. Both Eren and Annie could grow as individuals as they take on the responsibilities of parenthood. Additionally, the fanfiction could focus on the theme of unconditional love, as they start to feel this new kind of love for their unborn baby even before it's born.
I'm not sure if there is a specific fanfiction with such a storyline. Fanfiction can cover a wide range of themes and ideas, but this particular one might be quite rare or not widely known. You could try searching on specialized fanfiction websites.
There might be some fanfictions out there that deal with their relationship in a non - adult way. You could try searching on fanfiction - specific websites and filtering for the appropriate rating. For example, Archive of Our Own allows you to filter by rating such as General Audiences or Teen and Up. It's possible to find a story that focuses on their relationship developing in a more innocent way, perhaps with the idea of a future family in a very PG - 13 kind of concept.
Some fanfictions might center around their shared experiences in the Bleach universe. They could be on a mission together where they have to rely on each other's strengths. In these stories, the author might delve into how their different powers and personalities could work together towards a common goal. It's all about building a connection between them that is not based on adult or inappropriate content.
One possible plotline could be a story set in an alternate universe where Aizen has redeemed himself. He and Orihime fall in love and the pregnancy is a symbol of their new beginning and the hope for a better future. It could focus on how they prepare for the baby, dealing with the reactions of their friends and family in that universe.
One common theme could be the theme of responsibility. For example, both Ichigo and Byakuya having to step up and take care of someone new, whether it's a new life or just a new situation that is like having a new 'life' in their group. Another could be the theme of friendship. Their friendship might be strengthened as they go through this new experience together.
One common theme could be the theme of sacrifice. Edward Elric might be in a situation where his pregnancy is a result of some magical or alchemical sacrifice for a greater good, like saving his loved ones or his world. Another theme could be that of acceptance, where he has to come to terms with this unexpected state and the reactions of those around him.
One popular theme is the 'alternate universe' where the normal Hogwarts rules don't apply. In such a story, Hermione could be pregnant as a result of a unique magical experiment that Snape has to oversee. It's more about the mystery and adventure of the situation rather than any romantic or adult content. Another theme could be a 'curse - breaking' one, where Hermione is affected by a curse that gives the appearance of pregnancy, and Snape is the one with the knowledge to break it.
One common theme could be the exploration of Zuko's character growth. For example, becoming pregnant might force him to face his insecurities and learn to rely on others more. Another theme could be the reaction of his friends and family. How do they support or struggle to accept this new situation? It could also be about the challenges he faces in a society that may not be accepting of such a situation.
Often, there is the theme of survival. Sansa has to find a way to survive for herself and her unborn child. This can involve her making strategic alliances or using her wits. Also, the theme of hope might be present. The fanfiction could explore how she holds onto hope in a very difficult situation, believing that things will get better for her and her baby in the future. And then there's the theme of family, not in the traditional sense perhaps, but how she creates a new family or support system around her during this time.