Alec might also come to her rescue. As a skilled Shadowhunter, he has a strong sense of duty. Plus, he's part of Clary's group, and he wouldn't stand by and let a fellow Shadowhunter be attacked by a demon.
Another character who has a personal vendetta against Clary or her family. For example, a jealous rival or someone who blames her family for past misfortunes. This would add a layer of drama and personal conflict to the fanfiction.
Well, she might be rescued by her friends. In many fanfictions, her Shadowhunter comrades would come to her aid, using their unique skills to fend off the attackers.
A third plot twist could be that the attack is a diversion. While Clary is fighting the demon, something much more significant is happening elsewhere. Maybe a powerful artifact is being stolen or a key location is being infiltrated, and by the time she realizes it, she has to race against time to stop the real danger.
Jace would likely be an important character. Given his relationship with Clary, he would probably be deeply affected by the news of the baby. His reaction could range from shock to protectiveness.
Simon might be in a bit of a panic. Since he's her friend and also not as used to the dangerous situations as the other Shadowhunters. He'd try to do whatever he can to help, like getting help from more experienced Shadowhunters or trying to comfort Clary while she's in pain.
In this fanfiction, Clary is likely a newly introduced and attractive female character. However, without more context from the specific fanfiction, it's hard to say more about her personality or role in the story.
Her friends could also play a crucial role. If she has a group of loyal friends, they might band together to find her. They could use their knowledge of the area where she was last seen or any clues they can gather to track down the kidnappers and save her.
Well, often it's Clary, Jace, and Simon. Simon is Clary's best friend, and in some fanfictions, his relationship with Clary can make Jace a bit jealous, but at the same time, if Simon seems too friendly with another girl, Clary might also get jealous in a different way. It's an interesting triangle - like situation that can add a lot of drama to the fanfiction. And of course, Magnus Bane might also make an appearance and his flamboyant personality could somehow be involved in situations that lead to Clary's jealousy.
Another option is a group of demons who have a vendetta against Clary or the shadowhunters in general. They might use torture as a way to break her spirit and gain information about the shadowhunters' defenses.
On the other hand, there could be a glimmer of hope in their relationship. Maybe through the shared experience of the pregnancy, they start to see the good in each other. Clary might see a side of Sebastian that she never knew existed, and Sebastian might start to have real feelings for Clary and the baby, leading to a more complex and evolving relationship.