When writing a Conan x Haibara 'lemon' fanfic in an appropriate way, think about their personalities. Conan is smart and curious, and Haibara is complex and reserved. You can build a story around how they gradually open up to each other. Instead of using 'lemon' in a sexual sense, you can use it to create a mood. For example, a lemon - tree - filled garden where they have a deep conversation that reveals their true feelings for each other. Also, always keep in mind the target audience and the general tone of the Detective Conan series, which is more about mystery and friendship at its core.
To write a Conan x Haibara fanfic with a 'lemon' element but still keep it appropriate, you should emphasize their unique bond. Describe how they support each other in the face of danger. You could use the 'lemon' concept to represent a new or unexpected element in their relationship. For instance, a new discovery about their pasts that makes their connection stronger, like a lemon - scented memory that brings them closer together in a non - sexual, emotional way. And avoid any overly sexual or vulgar language and scenarios.