One major theme is the struggle between good and evil within Clary herself. She's torn between her normal self and the dark influence of Lilith. Also, the theme of loyalty comes up a lot. We see how Clary's loyalty to her friends and the Shadowhunter cause is tested as she gets involved with Lilith.
One great 'Shadowhunters Lilith and Dark Clary fanfiction' is 'The Darkening of Clary'. It really delves into the darker aspects of Clary's character when influenced by Lilith. The author does an amazing job of showing the power struggle between them.
One popular theme is their forbidden love. Since they are both Shadowhunters and there are rules about relationships within the Clave. Another theme is their quest for power. They are always looking for ways to become stronger to fight the greater threats to the Shadowhunter world.
Love is a very common theme. Since Clace is a couple, their relationship and the challenges it faces are often explored. Another theme is adventure. They are Shadowhunters, so they often go on quests and fight against demons.
One common theme is love. Magnus' relationships, especially with Alec, are often explored. Another is power. His magical powers and how they are perceived by the Shadowhunters are frequently a part of the stories. Also, acceptance. Magnus being a Downworlder, his fight for acceptance among the Shadowhunters and the mortal world is a common theme.
Friendship is another big theme. Characters from both universes form new friendships. In many fanfics, you'll see Kurt from Glee becoming friends with Alec from Shadowhunters. They learn from each other's strengths and weaknesses.
Love and relationships are also a big theme. When different universes collide in these crossovers, new love interests can be formed. It might be between a Shadowhunter and a character from another world, and this creates all kinds of drama and tension. It's not just about romantic love, but also friendship and loyalty among characters from different backgrounds. Another common theme is the fight against a common evil. Characters from different worlds might have to team up to defeat a powerful foe that threatens both of their universes.
Well, their relationship in the original series has a lot of potential for exploration in fanfiction. They start off as somewhat at odds with each other, but as they face common enemies and challenges, there is room for their relationship to grow and change in many different ways that fanfiction writers like to explore.
In some fanfics, Simon and Clary's love is a slow - burn type. They start as friends, but as they fight side by side against demons, they gradually realize their feelings are more than just friendship. For example, there could be a scene where Simon saves Clary from a particularly powerful demon, and in that moment of relief and gratitude, they share a kiss that changes everything between them.
Well, it's very probable. 'Shadowhunters' has a large and creative fan base. Given the popularity of the characters Clary and Alec, fans might be interested in writing about a moment like a kiss between them. However, the quality and nature of these fanfictions can vary greatly. Some might focus more on the emotional build - up to the kiss, while others might just include it as a part of a larger story arc.
There is a fanfiction called 'Alec's Perspective on Clary'. This one is interesting as it gives insights into Alec's thoughts about Clary. It shows how his initial wariness turns into a sort of begrudging respect and then friendship as they face different challenges in the Shadowhunter world.