Good character development. It should show how Ultra Magnus and Rodimus grow throughout the story, whether it's in their relationship or as individuals.
The fanfiction might be set in a post - war scenario. Ultra Magnus and Rodimus could be working towards rebuilding their world. There could be political intrigue as they try to re - establish order, with different factions having different ideas on how to move forward. And their friendship or partnership could be a key factor in uniting the Transformers during this difficult time.
One common theme is loyalty. Both Optimus Prime and Ultra Magnus are known for their loyalty to the Autobot cause. In fanfiction, this can be explored further, like in a situation where their loyalty is tested. Another theme could be leadership. How they lead the Autobots together or in different scenarios. For example, they might face a difficult decision on whether to sacrifice a small group for the greater good of all Autobots. And there's also the theme of friendship. Their relationship as comrades can be deepened in fanfiction, showing how they support each other through tough times.
Writers develop their relationship through shared challenges. For example, when they are on a mission to rescue captured Autobots. This forces them to rely on each other and builds trust. Another way is through dialogue. Meaningful conversations about their beliefs, goals, and fears can deepen their connection. Writers might also use flashbacks to show how their relationship has evolved over time, like an incident in their past that first brought them together.
One common theme is friendship. Since Magnus and Alex have a unique bond, many fanfictions explore how their friendship develops and deepens over time. Another theme is self - discovery. They both are complex characters, and fanfictions often show how they learn more about themselves through their relationship with each other.
One great Magnus Bane x OC fanfiction is 'A Shadowhunter's Heart'. It beautifully weaves the story of an original character into the Shadowhunter world. The relationship between Magnus and the OC is developed in a very natural way, with lots of emotional depth. Another one is 'Magnus and the Newcomer'. It has an interesting plot where the OC has a unique power that attracts Magnus. They go on various adventures together, and the chemistry between them is palpable.
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.
The development of their relationship. It should not be too rushed. A good fanfiction will show them gradually getting to know each other, facing challenges together, and falling in love. Maybe they start as enemies or just acquaintances and then slowly realize they have feelings for each other. Also, the setting in the Shadowhunter world can be used in creative ways. If the story is set in a different part of the Shadowhunter realm or during a special event, it can bring more excitement.
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.