One common theme is growth. Both Mondo and Chihiro are characters that can develop a great deal, and in fanfics, their relationship often helps them grow. For example, Mondo might become more understanding and less impulsive, while Chihiro becomes more confident.
Another theme is mutual support. They often find themselves in situations where they need to rely on each other. In some fanfics, this is shown through difficult school projects or dealing with personal issues. Their relationship evolves as they become each other's pillars of support, and this theme is central to many 'ishimaru x mondo fanfic' stories.
It could be the way the crime is depicted or the setting of Chicago that makes it stand out. Maybe the characters or the plot twists are what's unique.
One great Mondo x Chihiro fanfic is 'A New Bond'. It focuses on how Mondo and Chihiro's relationship develops in a post - game scenario. They support each other through the challenges of rebuilding their lives after the events in the game.
One great 'ishimaru x mondo fanfic' is 'The Unlikely Bond' which beautifully explores their relationship development. It shows how their different personalities gradually draw them closer.