One possible storyline could be a story of misdiagnosis. Kayano might be wrongly thought to be pregnant due to some strange alien or experimental side - effect in the Assassination Classroom world. This would lead to comical misunderstandings among her classmates and teacher, and the story could revolve around clearing up the confusion while also exploring her relationships with others.
There may be fanfictions that explore this idea in a family - friendly manner. Maybe it's set in an alternate universe where the 'pregnancy' is a result of some unique magical or scientific experiment that has nothing to do with adult situations. Writers often use such concepts to explore different aspects of a character's personality and how they would react in unexpected situations.
One possible plot could be a story about Nagisa and Kayano working together on a special project for the class. They might be assigned to plan a surprise event for Koro - sensei. Along the way, they discover new things about each other. Nagisa could learn more about Kayano's acting skills and how she uses them not just on stage but also in her daily interactions. Kayano could see Nagisa's determination and kindness up close, which deepens their friendship.
In a fanfic, their relationship might develop in a more romantic way. They could be paired up for a school dance or some other event. During this time, they have a chance to really talk and get to know each other on a more personal level. Nagisa might be shy at first, but Kayano's friendly nature breaks the ice. As they dance or spend time together, they feel a spark. This could be the start of a romantic relationship, with them stealing glances at each other in class and finding excuses to be around each other more often.
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.
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.
One possible storyline could be that Nagisa gets fatally injured during a particularly dangerous mission against a powerful new enemy that the class wasn't fully prepared for. Another could be that he sacrifices himself to save his classmates from a deadly trap set by the anti - Earth forces.
Another storyline could involve a character from Assassination Classroom being sent to the KHR world. Nagisa, with his assassin skills, could get involved in the mafia - like affairs of the KHR universe. He might use his stealth and combat abilities to help out the good guys in that world, or perhaps he gets caught in the middle of a power struggle between different mafia families.
Perhaps the pregnancy is a symbol of a new era of peace between the world of Frozen and Jack Frost's domain. Elsa and Jack Frost have to work together to prepare for the arrival of the baby. They might build a new place that combines the ice and snow elements of both their worlds, and in the process, they face challenges from those who oppose the union, but they overcome them through their combined powers and the power of friendship.
For Karma, he might start to show a more vulnerable side in the fanfiction. Usually, he's very confident and a bit of a troublemaker. But when it comes to Rio, he could become more hesitant and self - conscious, as he starts to really care about what she thinks of him.
If there are such fanfictions, themes could include the search for justice. Nagisa might be trying to seek justice against his abuser, which could involve him using the skills he learned in the 'Assassination Classroom'. Also, themes of friendship could be present. His classmates might notice the abuse and come to his aid, highlighting the importance of their relationships. Additionally, it could explore the theme of redemption for the abuser if the story takes that turn.