Often, there are themes of protection and support. Given the unusual situation of mpreg, Hide might be portrayed as being very protective of Kaneki. And also, themes related to the acceptance within the Tokyo Ghoul world or their own small community could be present. Since it's an unconventional concept, how other characters react to it can be an important part of the story. Additionally, themes of love and sacrifice might be emphasized as they face difficulties together because of the mpreg situation.
Finding specific Kaneki x Hide mpreg fanfiction can be a bit tricky. Firstly, not all platforms may support or have a large number of such niche fanfictions. However, AO3 is a great place to start. Use the search bar and type in 'Kaneki x Hide mpreg' and it will show you relevant works. Keep in mind that the availability might vary depending on the popularity of this particular pairing and concept within the fandom.
One idea could be a post - apocalyptic scenario where Kaneki and Hide are trying to survive in a world that has become even more hostile to ghouls. They could be on a journey to find a safe haven, relying on their deep - seated friendship and Hide's unwavering loyalty to Kaneki. Along the way, they face various challenges that test their bond.
Their relationship could be developed in a unique way by having Hide become a ghoul. This would completely change the power dynamic between them and force them to re - evaluate their friendship. They would have to learn to understand each other from a new perspective, as Hide now experiences the same struggles as Kaneki.
Unfortunately, Kaneki did die in the manga. This event was a turning point that brought about many changes in the storyline and the dynamics among the characters.