Well, in some of the light novels, there are plots involving strange codes. For example, a series of numbers and symbols left at the scene of a crime. Conan has to decrypt these codes which often lead to uncovering the identity of the culprit. He might draw on his knowledge of history, literature or even music to crack them. It makes for a really exciting read as we follow his thought process.
A plot could be that Shiho discovers a way to permanently reverse Shinichi's transformation, but the process requires them to go on a dangerous journey to find a rare ingredient. Along the way, they face many obstacles and grow closer as they rely on each other.
One interesting Detective Conan kidnapped fanfiction could be where Conan is kidnapped by a new, mysterious criminal organization. In this story, the kidnappers might be after his knowledge of the Black Organization. They could try to force him to reveal secrets, and Conan has to use his wits to escape while still in his shrunken form.
Some Detective Conan fanfiction novels are about time - travel scenarios. Imagine Conan going back in time to prevent the initial incident that led to him being shrunk. It's a really cool concept. Also, there are fanfictions where the Black Organization has different motives and more complex hierarchies. This can add a whole new layer of mystery and intrigue to the story. Oh, and fanfictions that feature crossovers with other detective or mystery series can be really interesting too.
One idea could be a fanfic where Conan has to solve a mystery within a virtual reality game world. Another could be a story where he teams up with a new character who has a unique detective skill that complements his own. Maybe a fanfic about Conan traveling back in time to solve a mystery related to his parents' past.
One interesting Detective Conan OC fanfic could be 'The New Detective in Beika'. It introduces a new original character who has unique deductive skills and gets involved in Conan's cases. Another great one is 'OC's Adventure in the Black Organization'. It gives a different perspective as the OC tries to infiltrate the Black Organization. And 'OC and Conan's Team - up' is also good, showing how an OC and Conan work together to solve mysteries.
One idea could be to write a fan fiction where Conan has to solve a mystery in an ancient, haunted castle. The castle could have secret passages and hidden rooms filled with clues that lead to a long - lost treasure. Another idea is to create a story where Conan teams up with a new character who has a unique skill, like being able to communicate with animals, which helps them solve the case in a different way. You could also write a fan fiction that takes place in a different time period, like the future, and Conan has to adapt his detective skills to new technologies.
One interesting detective conan baby fanfiction could be about Conan as a baby having some special powers that he unknowingly uses to solve mini - mysteries around him. For example, he might be able to communicate with animals in a way that gives him clues to find a lost item in the neighborhood.
Well, the love triangle involving Kazuha, Heiji and another character can be quite engaging. Kazuha has deep feelings for Heiji, but Heiji is often so focused on solving cases that he sometimes overlooks her feelings. This creates a lot of misunderstandings and tender moments between them as Kazuha tries to get Heiji to notice her more in the context of love rather than just as a friend in detective adventures.
Well, in some of the short stories, there are cases related to art theft. For example, a valuable painting goes missing during an exhibition. Conan notices small details like the behavior of the security guards, the layout of the gallery, and some peculiar marks on the wall near where the painting was displayed. By putting all these together, he's able to figure out who the thief is. It's really fascinating how he can solve such complex cases with just his observational skills and knowledge of crime.
One idea could be creating an OC who is a master of disguise, like Conan, but with a unique backstory. Maybe they are from a different country and have their own reasons for getting involved in the detective work in Japan. Another idea is an OC that has a special gadget - something that hasn't been seen in the original series yet, like a device that can analyze poisons instantly. And a third idea could be an OC who is a childhood friend of Shinichi's that has some hidden talents related to solving mysteries that come to light after his transformation into Conan.