To write their relationship realistically, you need to consider their personalities. Deku is kind - hearted and determined, while Shigaraki is more cynical and vengeful. So their interactions would be full of tension. For example, if they have an argument, Deku might try to reason with Shigaraki using his ideals, but Shigaraki would likely mock or reject them.
One interesting plot could be that Deku and Shigaraki, as brothers, are on opposite sides at first. But then they discover a common enemy that forces them to work together. This would involve a lot of character development as they have to overcome their differences. For example, Deku's belief in heroism and Shigaraki's hatred for the hero society.
In this fanfic, the relationship between Shimura Tenko and Uraraka Ochako could be full of interesting dynamics. Maybe it's a friendship that develops through shared challenges in the BNHA universe. They might support each other in battles or during their hero training.
To develop Tenko Shimura's character, consider his relationships. Maybe create a friendship or a mentorship for him in the fanfiction. This new relationship can force him to confront his beliefs and actions. Also, describe his physical and mental state as he uses his quirk. How does it affect him? Does it make him more detached from his emotions? All these aspects can help in developing his character.
One popular 'bnha shimura tenko x shinsou fanfic' is 'Parallel Paths'. It explores their relationship in a post - war setting where they both have to deal with the aftermath of the battles. The author does a great job of showing their growth and how they come to understand each other.
The uniqueness of bnha shimura tenko x shinsou fanfic lies in the combination of their personalities. Shimura Tenko has a complex and often misunderstood past, while Shinsou has his own insecurities and determination. When paired together in a fanfic, it creates a dynamic where they can either support each other's growth or clash in interesting ways.
Perhaps Shimura Tenko has some information that Uraraka Ochako needs for her own goals, like understanding a certain villain's motives. So, Uraraka Ochako tries to get close to Shimura Tenko to get that information, and in the process, a relationship forms. It could be a relationship filled with mistrust at first but then turns into something more positive as they get to know each other better.
The main differences are in their expressions and some minor details of personality. In the manga, Deku might seem a bit more intense, while in the anime, he's sometimes presented a bit softer.
You could write a fanfiction where Tenko Shimura is transported to an alternate universe where heroes and villains have different roles. In this universe, he might be forced to team up with heroes to survive. This would give a chance to explore his character in a new light, as he has to adapt to new rules and relationships while still dealing with his own inner demons.