Another idea might be a plot where the characters have to face a new, previously unknown threat that is related to the dark artifices but has a different origin. This could test their skills and relationships in new ways. Maybe it's a type of dark magic that was thought to be extinct but has been awakened.
A really engaging plot could be one where the main characters are transported to a different realm that is somehow connected to the world of 'Lady Midnight'. In this realm, they have to learn new rules and powers in order to find their way back home, all while dealing with the local inhabitants who may not be friendly.
One idea could be exploring the backstories of the minor characters in more detail. For example, the life of a downworlder who has interacted with the main characters but whose story is not fully told in the original. Another could be a 'what if' scenario, like what if a certain character made a different choice during a crucial moment in the story. This could lead to a completely different chain of events and relationships.
Emma Carstairs is likely one of the most popular. She's a strong and determined character in the original story, and in fanfiction, people often explore different aspects of her personality, like her relationships and her growth as a Shadowhunter.
Another plot could involve them facing opposition from the traditional good side, like Dumbledore's Army remnants. They have to use their newfound dark powers and cunning to outwit their opponents. Maybe they start to realize that the line between good and evil isn't as clear as they once thought. As they fight, they also discover secrets about the wizarding world's past that make them question everything they knew.
Some fan fictions might take a darker turn and explore what would happen if a powerful dark force overtook the Institute. This could lead to a situation where the main characters have to make difficult choices between their loyalty to the Shadowhunter laws and their own moral compasses, making for a very engaging read.
One idea could be exploring the backstory of the 'lady of darkness'. Maybe she was once a good - hearted being who was wronged and that led to her transformation. Another could be her forming an unlikely alliance with a hero to fight a greater evil.
One possible plot idea could be a story set in the midnight hours at Hogwarts. Maybe the main character, under the influence of the'midnight blues', discovers a hidden part of the castle that has been forgotten for centuries. It could be filled with ancient magic and secrets waiting to be unraveled.
One idea could be that Lady Death appears in the Naruto universe during a major battle. Maybe she's there to claim the souls of the fallen, but Naruto, with his unwavering belief in life and his friends, tries to convince her to spare them. This could lead to an interesting dynamic where Naruto has to prove the value of life to a being who has seen so much death.
Perhaps the story could focus on how their friends from the neighborhood react to the news. Some might be excited and offer help, while others could be jealous or worried about how it will change the dynamics of the community. For example, Jock might be overly protective and constantly check on Lady, while Peg could offer fashion advice for when the puppies are born.
One idea could be that the Lady of the Lake has a premonition about a great danger coming to Camelot and she enlists Merlin's help to prevent it. They have to go on a journey to find an ancient artifact that can save the kingdom.
Perhaps a fanfiction could focus on the backstory of Harvey Dent before he became Two - Face. It could show his early days as a prosecutor and how his idealism gradually got corrupted, which would add more depth to his character in the Dark Knight universe.