Well, one possible plot development could be that they initially avoid each other. Alec might throw himself into his work with the Shadowhunters, trying to forget Magnus. Magnus, on the other hand, could start traveling to different magical realms to distract himself. But as time passes, they might start to cross paths again, perhaps due to some common threat to the Shadow World. And slowly, they might start to remember the good times they had and question if the break - up was really the right decision.
In the 'alec and magnus after the break up fanfic', they could both go through a period of self - discovery. Alec might realize how much Magnus had influenced his view of the world outside of the strict Shadowhunter upbringing. He might start to explore more liberal ideas. Magnus, being heartbroken, could retreat into his magic studies and create new spells. But their friends might try to get them back together. Clary, for example, could see how much they still love each other and try to set up accidental meetings to make them talk again.
One reason could be miscommunication. Maybe they didn't fully understand each other's needs and wants. For example, Alec might be too focused on his shadowhunter duties and not give enough time to Magnus, who would then feel neglected.
Obviously, Alec and Magnus are the main characters. But new characters could also be introduced. For example, a new Shadowhunter trainee who looks up to Alec and tries to help him get over Magnus. Or a powerful warlock from another dimension who becomes Magnus' friend and tries to show him that there are other options besides Alec. There could also be a seer who predicts that Alec and Magnus are meant to be together and tries to nudge them in the right direction.
Some fanfics might show Alec being very stoic at first, hiding his pain. He's used to bottling up his emotions as a shadowhunter. But later, he might break down in private. For Magnus, he could be more openly heartbroken, showing his emotions through his magic, like making the room around him dark and stormy.
Maybe there was a big misunderstanding or some external pressure that made Magnus act that way.
One characteristic is the focus on the relationship between Alec and Magnus. It could be their romantic relationship, like in many fanfics where their love story is explored in great detail. Another is the exploration of their individual personalities. For instance, Alec's loyalty and Magnus's magic are often highlighted.
Well, perhaps the fanfiction could focus on how Magnus and Alec adjust to having a baby in their lives. Alec, being a shadowhunter, might have some traditional ideas about parenting which could clash with Magnus's more free - spirited and magical approach. And they could grow and learn from each other throughout the process.
One common way could be through using his magic in a subtle way. For example, he might use magic to create situations where Alec has no choice but to follow his lead. Maybe he makes it seem like the only option for Alec to protect his friends or family is to do what Magnus wants.
Love is a very common theme. Their relationship, which is between a Shadowhunter and a warlock, is full of challenges and the fanfics often explore how they overcome these through love. Another theme is acceptance. Alec has to accept Magnus's different lifestyle as a warlock, and Magnus has to accept Alec's duties as a Shadowhunter.
One possible plot could be that they meet by chance after a long time apart. Maybe at a Downworlder event where Magnus is using his magic to create some amazing display. Alec, who is there on some Shadowhunter business, can't take his eyes off Magnus. They exchange a few words, and the old feelings start to resurface.
Well, it could be a moment of intense emotion. Maybe they've been through a lot together, like fighting some great evil side by side. And in a moment of relief after a big victory, their eyes meet and they just can't hold back any longer. The kiss could be soft at first, full of unspoken feelings that have been building up for a long time.