Another idea is that it's all a dream - within - a - dream situation. Harry has a strange dream where Fred gets him pregnant, but when he wakes up, he's still in a sort of dream - like state where things are a bit off. The fanfiction could explore the psychological aspects of Harry's mind as he tries to figure out what's real and what's not, all while having this odd 'pregnant' state to deal with in the dream world.
One idea could be a magical mishap where a spell goes wrong and creates a false pregnancy situation for Harry. It could be a comical take on the situation as they try to figure out how to reverse it, with Neville feeling extremely guilty and Harry being more amused than angry.
One plot idea could be that Naruto and Temari are forced into an arranged marriage for political reasons between their villages. Over time, they start to understand each other better and develop real feelings. Then, through some magical or medical miracle, Temari becomes pregnant. Another idea is that they go on a dangerous mission together, get separated from their teams, and during that time, they make a deep emotional connection which leads to Temari getting pregnant later on in a very natural and story - appropriate way.
Perhaps there's a misinterpreted prophecy that leads to Tonks becoming pregnant. Harry and Tonks initially panic but then decide to work together. They could seek help from the Hogwarts professors. Dumbledore, for instance, might offer some wise advice on how to handle the situation. They might also have to deal with the reactions of their friends, like Ron and Hermione, who are initially shocked but then offer their support.
A possible plot could involve a parallel dimension. Percy and Artemis get pulled into a parallel dimension where the laws of nature are different. In this dimension, their powers interact in an unforeseen way and Artemis becomes pregnant. They must find a way to return to their own dimension while also dealing with the consequences of this new situation. They could encounter strange creatures and face unique challenges that test their abilities and their relationship.
Maybe in a fanfiction, there is a prophecy that foretells of a child born from Hermione and Tom that will bring great change to the wizarding world. This prophecy forces them to be together, and they have to deal with the prejudices of others. Hermione uses her knowledge to try and understand Tom's dark past better, and Tom, in turn, learns from Hermione's kindness. The pregnancy then becomes a central part of the story as they wait for the birth of this prophesied child.
One idea could be a magical pregnancy. Maybe a powerful spell backfires on Yugi or Yami, and as a result, they end up in a situation where they are about to become parents. This could lead to a whole adventure of finding a way to reverse the spell while also dealing with the emotions and changes that come with the unexpected pregnancy.
Perhaps in this fanfiction, Naruto and Korra find themselves in a situation where their pregnancies are part of a prophecy. They then have to figure out how to fulfill the prophecy while dealing with the normal challenges of pregnancy like mood swings and physical discomfort. They could meet other characters from their respective universes who help them on this journey, like Kakashi guiding Naruto on how to be a good father - to - be and Tenzin giving Korra advice on handling her new situation.
One possible plotline could be centered around the friendship aspect. Harry, Hermione, and Ginny might be worried about how their friendship will be affected by the pregnancies. They could work together to ensure that they still support each other through the changes. Another could be about how the wizarding community reacts. Maybe there are some old - fashioned views that they have to deal with, but they prove everyone wrong by handling the situation gracefully.
Perhaps there could be a time - travel plot. In the future, Bulma's grandchild (from Vegeta) discovers a way to go back in time. But something goes wrong during the time - travel, and it causes a strange energy reaction that makes it look like Goku is the father of Bulma's baby. Goku and Bulma then have to work together to figure out what happened and how to fix it. They go on a journey, facing challenges and meeting old enemies, all while trying to keep this strange situation a secret from their friends. In the end, they are able to correct the time - line and the false pregnancy situation.
One possible plot could be that a mischievous ninja casts a spell on Kiba as a prank. The spell makes Kiba's body go through changes similar to pregnancy, like gaining weight and having strange cravings. Naruto, being Kiba's friend, decides to help him find a way to break the spell. Along the way, they encounter various obstacles and have to use their ninja skills and wits to solve the mystery of the spell and reverse its effects.