One interesting female Kaneki fanfiction could be one where she forms an unexpected alliance with a group of ghouls from a different territory. In this story, she might use her unique perspective as both human and ghoul to bridge the gap between different ghoul factions. It could explore her internal struggle in a new light as she tries to maintain her humanity while also fitting into the ghoul world.
One possible fanfiction could be where Kaneki, after fully mastering his ghoul powers, becomes a sort of protector in the ghoul world. He could use his strength to keep the balance between humans and ghouls, defying the traditional enmity. He might be able to create new rules that both sides can abide by, making the world a more harmonious place for both species.
In a fanfiction where Kaneki is overpowered, he could have the power to heal the rift between humans and ghouls in a more radical way. He could use his extreme strength to force the humans to accept the existence of ghouls and also make the ghouls understand the importance of not preying on humans. His overpowered abilities would be like a shockwave that shakes the very foundation of the existing relationships and rebuilds them in a more positive way. For instance, he could create a safe zone where both humans and ghouls can live together without fear, and his overpowered presence would ensure that no one breaks the peace.
Self - acceptance is a very prevalent theme. The two Kanekis need to come to terms with their own existence and their relationship with each other. Identity crisis is also common. They both represent different aspects of Kaneki's identity and the fanfic often explores how to reconcile these different identities. Additionally, the theme of power and control can be seen, as they may fight over who gets to be in control in certain situations.
If Kaneki turns into a baby in fanfiction, it could be a way to explore his character in a new light. Maybe he retains some of his memories from his previous form, but is unable to communicate them clearly. This could lead to a lot of misunderstandings and new adventures. Also, it could be a chance for the author to develop new relationships for Kaneki, as a baby he would be more vulnerable and dependent on others.
I really like 'Kaneki's Female Companion'. In this fanfic, the female character has a unique backstory that intertwines with Kaneki's. It shows how their relationship develops in the dark and dangerous world of Tokyo Ghoul. The author does a great job of keeping the essence of the original Tokyo Ghoul while adding their own creative twists.
Kaneki and Touka could be in a situation where they have to team up with some former enemies to save the ghoul community from a new threat. This would test their ability to forgive and their leadership skills within the community.
A fanfic could focus on Rize teaching Kaneki how to fully embrace his ghoul side. She could show him how to use his powers more effectively and how to hunt without attracting too much attention. In return, Kaneki could teach Rize about human emotions and values, which she might have lost touch with over the years of being a ghoul. This exchange could lead to a deep bond between them.