There are quite a few good writers out there. One way to find them is to search for fanfiction communities dedicated to Naruto (since these characters are from Naruto). In these communities, people often recommend their favorite writers. Some writers are known for their in - depth characterizations of Itachi, Sakura and Shisui. They make the characters feel real and add new dimensions to their relationships. You might also want to follow some fanfiction blogs on Tumblr that often share and promote great fanfictions about these characters.
One possible fanfiction could be about Sakura joining an Anbu team that has Itachi and Shisui. Maybe Sakura is a new recruit and she has to learn from the two experienced shinobi. Itachi could be the calm and collected leader, while Shisui is the more easy - going one who helps Sakura adjust to the harsh Anbu lifestyle.
A common theme is time - travel. For instance, Sakura might travel back in time and meet a younger Itachi and Shisui. This allows for interesting plot developments as she tries to change the future or just understand their past better. Also, the theme of redemption can be found. Maybe Itachi or Shisui have made some mistakes in their past and Sakura helps them find redemption through their interactions with her.
The main characters are clearly Itachi, Sakura and Shisui. Itachi is the one who is amused, Sakura is the one doing the pummeling and Shisui is on the receiving end of Sakura's attack.
Sakura's amusement could actually make Shisui more likely to continue annoying Itachi. Since she finds it funny, Shisui might see it as a sign that his actions are acceptable and entertaining. This could potentially strain the relationship between Shisui and Itachi further if Itachi doesn't like being the target of Shisui's annoyance.
One idea could be a story where Sakura, as a skilled medic, is tasked with treating Itachi and Shisui during a difficult mission. She discovers their complex pasts and bonds with them over time, leading to new alliances and friendships.
A rogue ninja from a rival village could be the main antagonist. He might be after the secrets of the Sharingan that Itachi and Shisui possess. And he sees Sakura as an obstacle when she tries to protect her comrades. He could have some powerful and forbidden jutsu that makes him a formidable foe for the trio.
Well, I know that many fanfiction stories often explore unique relationships between these characters. For example, there could be a story where Sakura has to team up with Itachi and Shisui to face a powerful enemy. In these fanfictions, the authors might give Sakura new powers or abilities to make the story more interesting. Another common theme could be a love triangle between the three, which can lead to some really intense and emotional storylines.
To write a good fanfic, focus on character development. Let Sakura grow in her abilities and relationships. Show how Itachi's past affects his present actions when interacting with Sakura and Shisui. For Shisui, explore his loyalty and how that impacts the group dynamic. Also, use vivid descriptions of the Naruto world, like the Hidden Leaf Village or the battle scenes. This will make the fanfic more immersive.
She could develop a more strategic mind. Shisui and Itachi are known for their intelligence in battle. Sakura would learn from them how to analyze situations better, plan ahead, and anticipate her opponents' moves. This would make her a more well - rounded ninja rather than just relying on her brute strength.
Sakura's evolution would be quite remarkable. She would start to think more like an Uchiha. Their way of analyzing situations and opponents would seep into her own mindset. This could make her more calculating and less impulsive in battles. Her physical strength, which she already has a good amount of, could be refined further with the training she gets from Shisui and Itachi. Her social standing in the village might also change as she is seen training with two of the most powerful and respected Uchiha. People would start to view her as a serious combatant as well as a healer, and she would have a greater influence on village matters related to security and combat strategy.