One popular theme could be the growth and development of their baby. It might focus on the baby's magical abilities starting to show at a young age. Another theme could be family adventures, like the three of them going on a journey through a magical forest. Also, there could be themes about protecting the baby from threats, with Cadence and Shining Armor using their powers to keep their little one safe.
Writers can give the baby character some unique mannerisms. For example, a special way of giggling or a particular look it gives when it's curious. They should also consider the baby's limited understanding of the world around it, but still show that it has an instinctive connection to magic. And don't forget to make the baby react realistically to things like being held by its parents or seeing new and strange things.
Often, these types of fanfics can be a great way to expand on the characters. They might show a different side of Shining Armor, perhaps a more vulnerable side when it comes to protecting his family. And Cadence could be shown as not just a princess of love, but also a strong leader. The fanfic could also explore their friendships with other ponies in Equestria.
A good fanfic about them should have a strong plot. It could be about them solving a mystery in Canterlot. Also, the characters need to be in - character. Shining Armor should be brave and loyal, and Cadence should be kind and full of love.
I really enjoy Chrysalis and Shining Armor fanfics. They often explore unique relationships and scenarios. Some fanfics might focus on Chrysalis' complex character and how she could interact with Shining Armor in different ways, like in a world where she tries to reform. It's fascinating to see how authors play with their personalities.
Another theme is loyalty. Shining Armor's loyalty to Twilight and vice versa. They are always there for each other no matter what. This can be seen in fanfictions where one of them gets into trouble and the other drops everything to help.
One great fanfic is 'The Unlikely Bond'. It shows a very different side of Chrysalis as she and Shining Armor form an unexpected alliance. Another good one is 'Chrysalis' Redemption Arc' which focuses on Chrysalis' journey towards redemption with Shining Armor playing a crucial role in it.
The knight in shining armor manga usually features heroic knights with noble deeds and chivalrous values. The art style is often detailed and enchanting.
The family - bond trope is quite common too. Stories might focus on their relationship as siblings, how they support each other through tough times. There are also some fanfictions that use the trope of Shining Armor teaching Twilight about leadership, since he has his own experience in that area. These tropes are popular because they build on the existing relationship between the two characters in the My Little Pony universe.
You can start by looking on fanfiction platforms like FanFiction.net or Archive of Our Own. These sites have a large collection of fanfictions related to Twilight Sparkle and Shining Armor. Just search for their names in the search bar, and you'll get a list of various stories.