Another way to develop their characters is to put them in a situation where they have to make a difficult choice. For instance, they might have to choose between loyalty to their friends or following their hearts. This would force them to grow as individuals and as a pair. Their actions during this time would reveal more about their personalities and values.
One interesting plot idea could be that Kiba and Tsubaki have to team up for a special mission in the Underworld. They face various challenges and in the process, they discover new things about each other's pasts and their own powers. This could lead to a deeper bond between them.
Kiba could be developed by exploring his emotional side more. For example, showing his insecurities about his place in the group. This would make him more relatable.
For Asia, her character could be developed by exploring her past more deeply. Maybe she could have flashbacks to her life before joining the supernatural world, which would help explain her kindness and her eagerness to help others. As for Gasper, he could be made to overcome his extreme shyness. For example, by being put in situations where he has to speak up to protect Asia or their friends. This would show his growth and development.
Tiamat could be developed further by exploring her relationships with other characters. For instance, if she starts to mentor a young character, it would show a different side of her. She could teach them about her powers and the history of her kind.
One way is to introduce a new character who causes some sort of rift between them at first. Maybe a new devil who tries to drive a wedge between Rias and Akeno by spreading false rumors. But then, as they figure out the truth together, they become even closer than before. It would be a journey of trust - building and forgiveness that would enhance their relationship.
One common theme is character development. Writers often explore Tsubaki's growth, her relationships with other characters, and how she evolves within the Highschool DxD universe. For example, her relationship with the main character or her progress in her own powers.
For Issei, in fanfiction, he could be developed by giving him new powers. For example, he could gain some of Ophis' power in a special encounter. This would not only make him stronger but also force him to learn how to control and use it, which could lead to a more mature Issei. His relationships could also be developed further. With Ophis, he could start to understand her better and become more than just an acquaintance.
A common theme is Kiba's relationships. This can be his romantic relationships, like with a female character from the series. His friendships within the group are also explored a lot. The theme of redemption is also there. Kiba might be trying to atone for something he did in the past. And his role in battles, especially his strategic thinking and combat skills, is another common theme in Highschool DxD Kiba fanfiction.
One great female Kiba fanfiction is 'The New Path of Kiba Yuuto'. It explores a different side of Kiba where she has to face unique challenges in the Highschool DxD world. It delves into her character development in a way that the original series might not have fully explored.
Another option is to check out some anime - related forums. There are often threads where fans discuss and share their favorite fanfictions. For example, Reddit has some great anime sub - forums where you might find recommendations for Highschool DxD Tsubaki fanfictions. Some users might even post links directly to the stories they like.