One idea could be that Alec is really nervous about meeting Magnus' dad. Maybe he tries to learn all about Magnus' family history to make a good impression. He could bring a special gift that has significance in Magnus' family's culture.
Another plot idea is that Magnus' dad is initially skeptical of Alec. But as they start talking, Alec shows his deep love and commitment to Magnus. They could bond over their shared experiences of protecting the Shadow World. Alec might also share some of his own family values, which makes Magnus' dad see him in a new light.
A third idea is that there is some sort of magical or otherworldly problem that Alec and Magnus' dad have to solve together. This forces them to work as a team and in the process, they get to know each other better. Maybe there's a magical artifact that only Alec's Shadowhunter skills and Magnus' dad's warlock knowledge can unlock.
Well, perhaps it starts with a grand setting. Magnus has arranged for them to meet in a beautiful, magically - enhanced place. Alec walks in, a bit hesitant. Magnus' dad is there, with an air of mystery. Alec extends his hand for a handshake, but Magnus' dad just looks at it and then smiles and gives him a hug instead. Magnus is relieved and the conversation begins, with Alec stuttering a bit as he tries to introduce himself properly.
The meeting could introduce new elements to both storylines. In the Malec story, Alec could bring back knowledge of Lucifer's world that could change the power dynamics between the Shadowhunters and Downworlders. In Lucifer's story, Alec could be a catalyst for Lucifer to re - evaluate his own view of the world. He might see that there are other ways of being good and bad beyond his own understanding.
One idea could be that they adopt a young warlock who is having trouble controlling their powers. Alec and Magnus have to teach the child how to manage their magic while also protecting them from those who might want to use the child's power for bad. Another plot could be about adopting a mundane child and introducing them to the Shadow World. It would be full of discovery and the child learning about their new family's unique abilities.
One plot idea could be that Magnus and Alec go on a magical adventure together for the first time. They encounter a mysterious magical creature that is causing chaos in the Shadow World. As they work together to solve the problem, their relationship deepens. Another idea is that it's their first time attending a Downworlder - Shadowhunter event together. There they face some prejudice from both sides but their love for each other helps them overcome it. A third plot could be that they have their first real argument and then make up in a very romantic way, exploring more about their different personalities and how they can complement each other.
One plot idea could be the three of them going on a dangerous magical quest together. They have to face various challenges and in the process, their relationships deepen. Maybe Magnus uses his powerful magic, Alec shows his leadership and combat skills, and Jace his quick thinking.
One idea could be that Alec, from the Malec universe, stumbles into Lucifer's realm while on a mission. He's initially confused and on guard. Lucifer, being the charming devil he is, tries to make a deal with Alec. But Alec, being true to his Shadowhunter values, refuses. This could lead to an interesting dynamic where Lucifer is intrigued by Alec's integrity and Alec is both repelled and fascinated by Lucifer's world.
Maybe they get caught while using magic in a way that's not allowed in the public eye. They then have to face the consequences from the Shadowhunter authorities, which could lead to a whole adventure of trying to prove their intentions were good. They also might have to face the reactions of their friends and family who might be worried or disappointed.
One idea could be that Magnus kidnaps a Shadowhunter to force them to reveal a secret that could save the Downworld. He might believe this Shadowhunter has crucial information that the Nephilim are hiding. Another could be that Magnus is being controlled by a dark force and kidnaps someone as part of its evil plan. Then, the kidnapped person's friends have to find a way to break the control on Magnus and save their friend.
One interesting plot point could be the development of Alec and Magnus's relationship within the context of the City of Glass. Maybe they face some new challenges together that test their love. Another could be how they interact with the other characters from the original setting in this fan - made story.
A really cool plot could be that there's a prophecy that involves both Percy and Magnus. They initially don't trust each other but as they start to work together to fulfill the prophecy, they realize that they have more in common than they thought. Along the way, they might meet other characters from both of their stories, and there could be some epic battles and heart - warming friendships formed. There could also be a love interest involved, perhaps a character from one world falls for a character from the other world, adding a bit of romance to the mix.