Love and acceptance are very common. Given that they are from different worlds (Shadowhunter and warlock), their relationship often involves them learning to accept each other's differences. Another theme is family. Alec has his Shadowhunter family and Magnus has his own kind of 'found family' among the Downworlders. Fanfictions often explore how their relationship affects and is affected by their respective families.
Overcoming prejudice is also a big theme. In the Shadowhunter universe, there are prejudices between different species. Alec and Magnus' relationship challenges those norms. So, many fanfictions will show them facing and fighting against those prejudices, whether it's from other Shadowhunters or within the Downworlder community. It makes for some really intense and emotional storylines.
One of the most popular themes is the exploration of their cultural differences. Magnus being a warlock with a long and rich history and Alec being a Shadowhunter from a more traditional background. Another theme is their struggle against prejudice. They face discrimination from the Clave and others due to their relationship. Also, the theme of sacrifice is common, like how they would sacrifice for each other's safety and happiness.
There are also Tumblr blogs dedicated to sharing Alec Lightwood x Magnus Bane fanfiction. You can search for relevant tags and find some really unique and creative works that might not be as mainstream as those on AO3 or Fanfiction.net. These can offer fresh takes on their relationship, such as exploring how they handle cultural differences between the warlock and Shadowhunter worlds.
One great Magnus Bane and Alec Lightwood fanfiction is 'The Bond Beyond Magic'. It beautifully explores their relationship, delving into how their different personalities complement each other. Another is 'Alec's Discovery' which focuses on Alec's journey of self - discovery within the relationship. And 'Magnus' Heart' shows Magnus' perspective and his deep love for Alec in a very touching way.
A major theme in magnus x alec fanfiction is the exploration of power dynamics. Magnus is a powerful warlock and Alec is a shadowhunter. How they balance their different levels of power and influence in their relationship is often explored. Also, the theme of acceptance is quite prevalent. They come from different worlds, and their journey towards accepting each other's differences is a key part of many stories. For example, in some fanfictions, Alec has to come to terms with Magnus's long life and his different magical practices.
Well, in Magnus x Alec lemon fanfiction, a frequent theme is the discovery of each other's desires. Since they come from different backgrounds, Magnus being a warlock and Alec a Shadowhunter, there's a lot of room for exploring how they understand and fulfill each other's needs. Additionally, themes of acceptance, both within themselves and from their respective communities, are quite common. The 'lemon' aspect can sometimes be used to show the deepening of their bond and the breaking of barriers between them.
Another theme is the search for support. Alec usually has to find people he can trust to help him deal with the abuse. This could be his family members like Izzy or Jace, or new friends he makes along the way.
One common theme is vulnerability. Alec is often shown as a strong and stoic character in the original series, but in hurt fanfiction, his vulnerability is explored. For example, when he's physically injured, we see a different side of him that's more reliant on others for help.
Power is also a big theme. Alec's power as a shadowhunter is compared and sometimes combined with the powers in the crossover world. For instance, if he's in a X - Men crossover, how his rune - based powers interact with mutant abilities. And there's usually a theme of discovery. He discovers new things about himself and the new world he's in, which is often a journey of self - growth.
One common theme is love and relationship development. It shows how Magnus and Alec's relationship grows and overcomes various obstacles. Another theme could be adventure, where they go on quests together while being in a relationship.
Another theme is the struggle against prejudice. Since they are from different 'worlds' in the story, they face a lot of judgment from others, and fanfictions often deal with how they overcome this. Also, the theme of self - discovery is quite common. Both characters grow and learn more about themselves through their relationship with each other.