One idea could be to explore the backstories of the minor characters in more detail. For example, the character who only appears briefly in the original but has a really interesting look or a single line that makes you wonder about their past.
The 'jigokuraku light novel' is also known for its engaging plot. It weaves together elements of action, mystery, and drama. There are often unexpected twists and turns in the story that keep the readers on the edge of their seats. The pacing is well - managed, with a good balance between slower, more character - focused moments and fast - paced, action - packed sequences.
There's a fanfic called 'Gabimaru and Sagiri: The Unlikely Alliance'. In this one, they start off as reluctant partners but gradually form a deep connection. The author does an amazing job of showing Gabimaru's protective side towards Sagiri and how Sagiri comes to respect Gabimaru's skills and determination. It has some really intense and emotional scenes that make it a great read.
Begin by creating a basic outline. Decide on the main plot points, like who the protagonist will be, what their goal is, and what obstacles they'll face. For a jigokuraku fanfic, you might want to consider how the unique elements of the jigokuraku world will factor into your story. Then start writing the first chapter, introducing the setting and the main character. As you write, let your creativity flow and don't be afraid to deviate from your outline if a better idea comes along.
Characterization is key. A good Gabimaru x Sagiri fanfic should accurately portray their personalities. Gabimaru is tough yet has a soft side, and Sagiri is strong - willed and determined. If the fanfic can show how they complement each other, it's great. For example, Gabimaru's combat skills and Sagiri's strategic mind working together.