One interesting plot idea could be that Rima and Senri go on a secret mission for the vampire council. They have to face a group of rogue vampires who are threatening the peace between vampires and humans. Along the way, they discover a long - hidden power within themselves that helps them in the fight.
A plot could be that Senri and Rima get separated from their vampire group during a battle with a rival group. They have to rely on each other to survive in the wild and find their way back. This would force them to communicate and understand each other better.
Perhaps they fall in love in a fanfiction. Senri could be the one to break through Rima's cold exterior. They could have a story where they are forced to hide their relationship from the rest of the vampire community because of some old - fashioned rules. In this story, they would have to find ways to be together in secret, which would add a lot of drama and tension.
A really interesting plot could be a sort of 'what - if' scenario. For example, what if Shiki and Rima were to switch their roles or abilities? How would they adapt to this new situation? It could lead to some really creative storytelling, with them having to deal with the challenges and advantages that come with this role - reversal while still maintaining their bond.
They could be paired up for a school project in the Vampire Knight world. Senri, who isn't very talkative, and Takuma, who is more outgoing, would have to find a way to work together effectively. This could lead to some comical situations as Senri tries to keep up with Takuma's enthusiasm.
Another way to develop their relationship is by having them face a conflict within the vampire community. Maybe there is a new rule that they both disagree with. Standing up together against this rule would strengthen their bond. Senri could be the more hesitant one at first, but Rima's determination could inspire him, and they would grow closer as they fight for what they believe in.
One possible fanfiction could be about Senri and Takuma going on a secret adventure in the Vampire Knight world. Maybe they discover a hidden part of the school that holds a powerful vampire relic. They have to work together to keep it safe from those who would use it for evil purposes.
In a fanfiction, Rima and Shiki could start as rivals. Rima might see Shiki as a threat to her position among the vampires. But then, they get paired up for a task that requires them to work together. As they spend time together, they start to understand each other better. Shiki realizes that Rima is not as cold as she seems, and Rima sees that Shiki has a kind heart beneath his tough exterior.
A story could be about Rima and Shiki exploring an ancient vampire tomb. There, they find clues about their vampire lineage that they didn't know before. This discovery could change their relationship as they realize they are more connected than they thought.
A more action - packed plot could be the red knight leading a rebellion against the vampire hierarchy. They gather other vampires and humans who are tired of the oppression and fight for a new order. Along the way, they discover secrets about the vampire world that could change everything.
A possible plot is that a dark force in both the Inuyasha universe (connected to Kagome) and the Vampire Knight world is trying to take over. Kagome and the main characters from Vampire Knight, like Zero and Kaname, have to work together. Kagome's knowledge of magic and spiritual energy could be combined with the vampires' powers to combat this threat. They might start off distrusting each other but gradually learn to rely on one another.