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.
You can try some popular fanfiction websites like Archive of Our Own (AO3). It has a large collection of fanfictions in various fandoms, and you're likely to find some great magnus x alec x jace ones there. Just use the search function on the site.
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.
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.
The popularity might be due to the dynamic between the two characters. The alpha - omega relationship often brings an interesting power dynamic and a lot of room for romantic and dramatic storylines.
One great 'magnus x alec fanfiction' is 'The Bond of Magic and Love'. It beautifully portrays their relationship development with well - written dialogues and vivid descriptions of their magical world. Another is 'Magnus and Alec: A Journey Together' which focuses on their adventures side by side, showing how they support each other through tough times.
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.
One more theme could be the struggle against the norms of their society. In some fanfictions, the alpha - omega dynamic might be strictly defined by society. Magnus and Alec could be fighting against these norms, whether it's about how omegas are supposed to behave or who alphas can be with. This theme allows for some interesting plot developments as they try to carve out their own path together.
Sure. You can try searching on Archive of Our Own (AO3). It has a vast collection of fanfics, and you're likely to find many 'magnus x alec' fanfics there. Just type in the relevant tags in the search bar, and it will show you a list of stories.