One interesting plot idea could be a story where Rentaro and Kisara have to go on a secret mission outside the known safe zones. They face new types of Gastrea that they've never encountered before and have to rely on each other's unique skills to survive. Maybe Kisara discovers a new power within herself during the mission, and Rentaro has to figure out how to incorporate that into their battle strategy.
Perhaps a time - travel plot where Rentaro and Kisara are sent back to a time before the Gastrea outbreak. They then use their knowledge of the future to try and prevent the whole disaster from happening. But they face challenges like being believed by the people of that time and also not changing the future in a way that could be even worse. They have to balance their desire to save the world as they know it with the potential consequences of their actions.
A plot could revolve around Rentaro getting injured severely and Kisara having to take on a more leading role. She has to deal with the political aspects within the community as well as the threat of the Gastrea. Meanwhile, she's constantly worried about Rentaro's recovery and this adds an emotional depth to the story. For example, she might have to make tough decisions about whether to continue with a certain plan that could endanger Rentaro further if he tries to join in too soon.
Rentaro and Kisara could be forced to participate in a dangerous tournament where they have to fight against other pairs. They train hard together, and during this time, their relationship deepens. They develop a unique fighting style that combines their skills and helps them win the tournament.
One possible fanfiction could be where Rentaro and Kisara go on a mission together outside the protected area. They face a new type of Gastrea that they've never encountered before. During the battle, Rentaro realizes his growing feelings for Kisara as he sees her fight bravely to protect him. In the end, they defeat the Gastrea and their bond grows stronger.
A possible plot could be Rentaro and Kisara going on a mission together to rescue some Civilians from the Gastrea. During the mission, they face various challenges and have to rely on each other's skills. Their relationship deepens as they overcome these obstacles.
Their relationship can be developed by having them share more personal stories. For example, Rentaro could open up about his past traumas regarding the Gastrea war, and Kisara could do the same about her family or her life before they met. This would create a deeper emotional bond.
I'm not sure where you can specifically find a 'Black Bullet' fanfic about Rentaro and Kisara with 'lemon' content (which often implies adult or inappropriate themes). Fanfics with inappropriate content are not allowed on many official platforms. You could try looking on general fanfic websites but be aware of their terms of use.
A trope that I've seen a fair bit is the 'alternate universe' one. In these fanfictions, Rentaro and Enju are placed in different settings, like a high - school AU or a fantasy AU. It's really interesting to see how their characters adapt to these new environments while still maintaining the core of their relationship. It gives the writers a chance to explore different aspects of their personalities and how they would interact in different situations.
One great Rentaro and Enju fanfiction is 'A New Day'. It explores their relationship in a post - apocalyptic world. It shows how they grow together and face new challenges. It has really good character development for both of them.
One idea could be exploring the backstories of the cursed children in more detail. For example, you could write about a cursed child's life before she was paired with a promoter. Another idea is to create an alternate ending to the story, where the situation between the Gastrea and humans is resolved in a different way.
A great Rentaro x Enju fanfiction often has well - developed characters. It should stay true to their personalities from the original anime. For example, Rentaro's determination and Enju's innocence should be intact. Also, an interesting plot that explores their relationship further, like dealing with the challenges they face together in the post - apocalyptic world of Black Bullet.
Well, the characters in 'Black Bullet Kisara Light Novel' are quite fascinating. Kisara, for example, has a complex personality that evolves throughout the story. The world - building is another great aspect, with its unique post - apocalyptic setting where humans fight against the Gastrea. The plot often keeps you on the edge of your seat with various twists and turns.