Narcissa Malfoy could be an interesting character to include. She might be torn between her loyalty to the Malfoy family traditions and seeing the potential good in Harriet for her son. She could play a role in bringing Harriet and Draco closer, perhaps by inviting Harriet to the Malfoy manor under some pretext, which would be a very tense and interesting situation.
Dumbledore could also be included. He could be the one who sees the potential for a positive change in the relationship between Harriet and Draco. He might give them subtle hints or tasks that force them to work together and understand each other better, all while guiding them towards a better future for the wizarding world.
Hermione would be a great addition. She could be the voice of reason and also use her vast knowledge of magic to help Harry and Draco in their high - stakes situation. For example, when they are facing a complex magical puzzle as part of their mission.
Harley Quinn could be a great addition. She has a complex relationship with both Poison Ivy and Batman. Her chaotic nature could add a lot of twists to the story. Another character could be Alfred. His wisdom and loyalty to Batman could provide interesting interactions when dealing with Ivy.
Edward could be a good addition. Since he has his mind - reading ability, it could create some interesting interactions with Alice's visions. Also, Bella could be included as she has a connection to both Alice and Jasper through Edward. Her human perspective could add a different dimension to the story.
Well, Kikyo is an obvious choice. Her connection to both Inuyasha and Naraku is deep. Her presence could create a lot of tension, especially since Kagome is often compared to her. Shippo could also be in the fanfiction. His cute and innocent nature could contrast with the dark nature of Naraku. And Kaede, the old priestess, could offer her guidance and wisdom regarding the strange relationship between Naraku and Kagome.
Lois could be a great addition. Her relationship with Peter and her reactions to his antics with Quagmire can add a lot of drama. Also, Cleveland. His calm and collected nature contrasts with Peter and Quagmire's craziness. His interactions with them can lead to some really funny moments.
I think Hinata could be a great addition. He could be the comical sidekick who always gets into funny situations and in the process, either helps or hinders Usui and Ayuzawa's relationship. Another good character could be Ayuzawa's mother. Her presence could add some family drama, like she might not initially approve of Usui for her daughter.
Hermione could be included. She might be suspicious of Harry's interactions with Bellatrix and try to interfere or help, depending on the situation. Her intelligence could also be crucial in understanding any strange magic related to Bellatrix.
Jacob could be a great addition. He has a complex relationship with Bella in the original series. In fanfiction, his interactions with Charlie could be explored further. For example, how Charlie reacts to Jacob's wolf - shape - shifting abilities and his love for Bella.
Santana could be a great addition. She could be Rachel's best friend who gives her brutally honest advice about married life. Like when Rachel has a fight with Jesse, Santana would be there to say something like 'Girl, you need to put your foot down or he'll walk all over you.'
Edward could be included. He could be Emmett's rival in a sense, not in a romantic way towards Rosalie, but perhaps in a career or talent aspect. For example, if Emmett is into sports, Edward could be a really good athlete too. This creates some friendly competition between them. Also, Leah could be a character. She could be Rosalie's coworker and through their friendship, Leah could influence Rosalie's relationship with Emmett in different ways.