A 'lock and key novel' is a type of novel that often involves elements of mystery or secrecy. It might be centered around a locked room mystery, where the key to solving the mystery is like a key in a lock, unlocking the secrets within the story. For example, in some detective novels, the detective has to find the key piece of evidence (the 'key') to unlock the truth about a crime (the 'lock').
I'm not sure specifically as I haven't read it in detail. But generally, a 'lock and key' concept in a graphic novel might involve themes of mystery, like finding the right key to unlock a secret or solve a problem.
There could be a situation where a little girl, while playing a prank on her brother, secretly stuck his key inside the lock of his bicycle. She thought it would be funny to see his reaction. But her brother got really angry when he couldn't unlock his bike to go to his friend's house. In the end, she apologized and they found a way to get the key out together.
I don't know the main characters in 'lock and key graphic novel' as I haven't read it. You could try looking for reviews or summaries online to find out.
In 'under lock and key fanfiction', it may deal with power dynamics. For example, one character might have another character under their control, much like something being locked away and only accessible or manipulable by the one with the key. It could also be about a hidden society or group that is 'under lock and key', meaning it's very exclusive and secretive, and the fanfiction explores the inner workings of this group.
One example is 'The Murders in the Rue Morgue' by Edgar Allan Poe. It has elements of a locked room mystery which is a characteristic of a 'lock and key novel'. Another is 'And Then There Were None' by Agatha Christie, where the mystery on the island is like a locked enigma and the detective has to find the keys to solving the murders.
Start by looking on popular fanfiction platforms. AO3 is known for its wide range of fan - created works. Just use the search function and type in 'under lock and key' and see what comes up. Also, some smaller, niche fanfiction communities might also have such stories. You could search for forums or groups dedicated to the fandom that might be related to this fanfiction and ask around there.
In 'under lock and key miraculous fanfiction', a frequent theme is struggle. The characters are likely to struggle against their confined situation. It could also involve themes of discovery. As they try to break free from being locked away, they might discover new things about themselves, their powers, or the Miraculous world in general. For example, they could find out about a long - lost power or a hidden enemy. And of course, there's the theme of trust. They may have to trust in new allies or their own instincts to get out of the locked - in situation.