A major theme is also the exploration of different cultures within the two fictional universes. The ninja world of Naruto and the martial arts world of Kenichi have their own unique cultures. Fanfic writers often use this to create interesting scenarios. For instance, they might have Kenichi participate in a ninja festival in the Naruto world, or Naruto train in a traditional martial arts dojo in Kenichi's world. This theme of cultural exchange adds depth to the stories.
Another great 'kenichi x naruto fanfic' is 'Bonds Beyond Series'. This fanfic focuses on the friendship that develops between Kenichi and Naruto. It shows how they start off as strangers from different fictional universes but gradually form a strong bond as they face various trials and tribulations together. They both grow as characters in this story, with Naruto teaching Kenichi about chakra and Kenichi showing Naruto some new martial art moves.
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.
One popular 'kenichi fanfic' could be 'Kenichi's New Adventure' which might explore new martial arts challenges for Kenichi. Another could be 'Kenichi and the Mysterious Ally' where he teams up with an unexpected character. There are also some fanfics that focus on Kenichi's relationships, like 'Kenichi's Growing Bonds' which delves into his friendships and how they evolve over time.
Loyalty is another common theme. They are loyal to their friendship and to their respective martial arts schools. In some fanfictions, this loyalty is tested, such as when they have to choose between their friendship and the rules of their schools, but they always find a way to stay true to each other.
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.
One popular takeda x kenichi fanfiction is 'The Bond of Training'. It focuses on their journey of training together and how their relationship evolves. It has great character development and some really intense fight scenes that add to the overall story.
First, you need to be familiar with the 'Kenichi' universe. Know the characters, their personalities, and the rules of the martial arts in the story. Then, come up with an interesting concept, like a new enemy for Kenichi or a different kind of training he could undergo. After that, start writing, making sure to keep the dialogue in line with how the characters speak in the original.
Another theme is the OC's role in the conflict within the Kenichi world. Whether it's helping Kenichi and his friends fight against a new enemy or getting involved in internal disputes among different martial arts groups. This theme shows how the OC can impact the pre - existing story structure and bring new twists to the narrative.
Often, they highlight the contrast between Kenichi's more naive and determined nature and Shigure's more experienced and mysterious side. Their love is shown as something that bridges these differences.