One possible plotline could be that they are forced into an unexpected situation where they have to deal with the pregnancy together despite their differences. Another could be that it's a result of some magical or mysterious event that binds them in this situation, and they must navigate their new relationship while also dealing with the reactions of the Avatar world.
In the official Avatar universe, Tarrlok and Korra have a rather adversarial relationship at times. So a fanfiction about them being pregnant is quite a departure. But it could be an interesting concept for those who like to dig deeper into character relationships. Some fans might use it to explore themes of redemption for Tarrlok or a different side of Korra's character. However, overall, it's not a mainstream idea within the fandom.
There's also 'The Bond with Korra'. This one stands out because it delves deep into the emotional connection between Korra and the reader. It shows how they support each other through tough times, and the writing style makes it a very immersive read.
Ichigo's Soul Reaper powers are based on spiritual energy, and Korra's bending is based on her connection to the elements. Their powers could interact in a way that creates a new form of energy. For example, when Ichigo uses his Getsuga Tenshou near Korra while she's bending, it might create a shockwave that combines the force of the spiritual energy blast with the element she's bending. This could be a very powerful and unique combination that they could use to defeat enemies.
There are likely to be some out there. However, the quality can vary greatly. Some fanfics might focus on their friendship, while others could explore more creative or alternate universe scenarios between Korra and Katara. It's a matter of exploring different platforms and reading reviews if available to find the good ones.
One common theme is the exploration of their different backgrounds. Korra is from the South Pole and Asami is from a more urban, technological background. Fanfictions often play with how these differences bring them together.
One great 'Aang x Korra fanfic' is 'The Avatar's Legacy'. It beautifully weaves together the different eras of Aang and Korra. The story has a great plot where they have to team up to face a new threat that combines the old and new evils in their world. The character development is on point, showing how their different personalities and experiences complement each other.
Love and friendship are very common themes. Most fanfics focus on how Korra and Asami's relationship grows from being friends to something more. They often show how they support and understand each other.
A common theme is friendship evolving into love. Many fanfics start with their strong friendship, like in the show, and then show how that bond deepens into romantic feelings over time.
A common theme is the exploration of their age - gap relationship. Tenzin is much older, so there's often a focus on how they bridge that gap. Another theme is the clash between Tenzin's traditional airbending wisdom and Korra's more impulsive Avatar ways.