Well, the theme of duality is everywhere in these fanfics. It's about the two sides of Kaneki co - existing. Another important theme is redemption. Sometimes one Kaneki may try to redeem the other. And the theme of unity also exists. There are fanfics where the two Kanekis eventually unite to face a greater threat. Also, the exploration of the mind and consciousness is a common theme as it's related to Kaneki's complex nature.
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.
The theme of friendship in the face of adversity is quite common. They are in a world full of conflict between ghouls and humans, yet they form a connection. There's also the theme of sacrifice. In some fanfics, one may sacrifice for the other to uphold their new - found relationship or to protect the greater good in the Tokyo Ghoul universe.
One common theme is the exploration of their complex relationship. Given their different personalities and backgrounds within the Tokyo Ghoul universe, fanfics often focus on how they interact, whether it's a love - hate relationship or a gradual understanding and acceptance.
Love and acceptance are very common themes. Given that Kaneki is a half - ghoul and Touka is a full ghoul, their relationship often explores how they accept each other's differences.
I've heard of a fanfic named 'Eyes of the Self'. In this one, the two Kanekis are constantly at odds, yet they also have a deep understanding of each other. It's really well - written, with great descriptions of their internal battles. There's also a fanfic that's more action - oriented called 'Battle of the Kanekis' where they fight against a common enemy while also dealing with their own relationship. And 'The Kaneki Bond' is a heart - warming fanfic that shows the bond between the two Kanekis growing over time.
Many Kaneki x Tsukiyama fanfics also tend to be set in the dark and gritty world of Tokyo Ghoul. The setting adds to the overall atmosphere of the relationship. The fanfics might include elements like their interactions within the ghoul society, their battles together or against each other, and how these experiences shape their relationship. For example, a fanfic could show how they bond over a shared enemy or a difficult situation in the ghoul underworld.
One common theme is the struggle for identity. Female Kaneki, being both human and ghoul, constantly has to figure out who she really is. This is often explored through her interactions with both humans and ghouls, and how she feels like she doesn't fully belong to either group.
The theme of redemption can also be present. Rize's actions towards Kaneki were quite cruel in the original story. Fanfictions may attempt to give her a chance at redemption, perhaps through her relationship with Kaneki. This could involve her showing remorse for what she did and trying to make amends in some way.
One common theme is love and sacrifice. Kaneki and Touken's relationship is often depicted as a deep, selfless love. They might be willing to sacrifice their own safety or desires for the other. For instance, Kaneki could put himself in danger to protect Touka from a powerful enemy.
Common themes in fanfictions about their love include growth. Both Kaneki and Touka grow as individuals because of their relationship. They become more empathetic and stronger. Another theme is the exploration of the forbidden. Their love is a bit of a taboo as a ghoul - human relationship (even though Kaneki is half - ghoul). It adds an element of excitement and danger to their story. And unity is also a theme, as they unite against the forces that try to tear them apart and the discriminatory world around them.
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.