A sense of loyalty is often a theme. In these fanfics, Shinra and Tamaki are shown to be loyal to each other. Whether it's facing external threats or internal doubts in their relationship, they stand by one another. And the theme of shared dreams can also be found, like they might have a common goal for the future.
I like the fanfic 'Shinra and Tamaki: A New Beginning'. In this one, it starts with a new situation for both of them. It explores their feelings in a fresh way, like how Shinra first realizes his deeper feelings for Tamaki and how Tamaki responds to his newfound affection.
Another plot could involve Tamaki getting injured during a fight. Shinra then takes it upon himself to take care of her. As he nurses her back to health, they have a lot of time to talk and get to know each other on a more personal level. This could lead to them realizing that they have a lot more in common than they initially thought, and their relationship could grow from there.
In a fanfic, their relationship could also develop through moments of vulnerability. Let's say Shinra has a nightmare about his past and Tamaki is there to comfort him. Or Tamaki has a moment of self - doubt about her abilities, and Shinra gives her an encouraging speech. These moments of showing their true selves and being there for each other can deepen their connection. It's about creating situations where they can be honest with each other and build an emotional bond.
One common trope could be 'opposites attract'. Tamaki might be outgoing while Shinra is more reserved, and this contrast can create an interesting dynamic in a love story. Another could be 'friends - to - lovers'. They start as friends, gradually realizing their deeper feelings for each other.
You can try websites like Archive of Our Own (AO3). It has a large collection of fanfictions from various fandoms, and there's a good chance you'll find Tamaki and Shinra love fanfiction there.
Love and loyalty are very common themes. Celty and Shinra have a deep love for each other that is often the focus. Fanfics show how they are loyal to one another through various situations. Also, the theme of discovery is there. As Celty discovers more about the human world through Shinra, and Shinra discovers more about Celty's true self, these aspects are frequently written about in the fanfics.
A common theme is the exploration of their opposite personalities. Hibana is more reserved and Shinra is brash, so fics often play with how they interact with and complement each other.
Love and loyalty are often themes. Shinra is always very loyal to Celty, and their love story, which is quite unique given Celty's nature, is a central part. Also, the theme of discovery. Celty is constantly discovering more about the human world with Shinra by her side, and Shinra is learning about Celty's world as well.
Often, there are plotlines where they have to deal with misunderstandings between them. For instance, Arthur might misinterpret Shinra's actions, leading to a rift in their relationship that they then have to repair. There are also plotlines where they are pitted against a common enemy that forces them to work closely together and understand each other better, strengthening their bond.