After killing his lover, Itachi may become a more complex and brooding character. His relationships with other characters would be severely strained. For instance, if he had a mentor, the mentor might be disappointed in him. The death of his lover could also be the catalyst for a new conflict. Maybe there are people who want revenge for her death, and they start to target Itachi and his allies, leading to a series of battles and power struggles in the fanfiction.
The story might develop with Itachi seeking redemption in some way. He could start to perform heroic deeds to atone for what he did. Or, on the other hand, he could be hunted by those who were close to his lover. His actions could also trigger a chain of events that expose some hidden secrets in the world of the fanfiction, like secrets about his clan or the political situation in their land.
Perhaps in the fanfiction, his lover was involved in something dark that Itachi couldn't tolerate. For example, she might have been collaborating with the enemies of Itachi's clan. So, to preserve the honor and safety of his clan, he made the difficult decision to kill her. It could also be that Itachi was misinformed about his lover's actions and later regretted it deeply.
If it's a 'itachi becomes hokage fanfiction', the development would be interesting. Itachi, as Hokage, would probably try to atone for his past sins against the Uchiha clan. He could start initiatives to honor the clan and integrate the remaining Uchiha members into the village's core. Along the way, he'd have to deal with political intrigue from other villages who might see his new position as a threat.
He could also develop through facing new threats in the RWBY world. The Grimm are different from his usual opponents in Naruto. Dealing with them might force him to adapt his combat style and in turn, grow as a character. For instance, he might have to rely more on others' skills in a team - based RWBY battle scenario.
At first, they might be at odds with each other. Itachi is cold and distant in his Anbu ways, while Sakura is full of passion. But when they are in a life - or - death situation together, they start to understand each other better. Sakura could show Itachi the importance of having emotions in their line of work, and Itachi could show Sakura how to be more strategic.
It's got great character development and a compelling story. The way the relationship between the characters is portrayed is really engaging.
At first, Naruto might be a bit hesitant to work with Itachi because of his reputation. But Itachi's calm and calculated approach to their missions slowly wins Naruto over. They start to share their stories, with Itachi telling Naruto about his past and the Uchiha clan. This sharing of personal experiences deepens their bond, and they become more than just comrades in arms. They start to see each other as friends who can rely on one another in difficult situations.
At first, it could be a bit awkward. Sarada has only heard stories about Itachi. But as they start to interact, they might develop a mentor - mentee relationship. Itachi could see Sarada's potential and start to guide her.
In many fanfictions, Sasuke starts as a character full of anger and a thirst for revenge. But in the context of a relationship with Itachi, he begins to soften. He starts to see Itachi in a different light, beyond just the person who killed their clan. Itachi, on the other hand, is often portrayed as a complex figure with many secrets. In these fanfictions, his love for Sasuke makes him more vulnerable and human. For example, in some stories, he reveals his true motives to Sasuke, which changes their dynamic.
At first, it's likely to be very awkward. Naruto is a very open and energetic person, while Itachi is more reserved. But as they are forced to spend time together because of the arranged marriage, they start to find common ground. For instance, they both care deeply about protecting the village in their own ways.
Itachi would be very strict in Naruto's training, but also very caring. Naruto would look up to Itachi and try to learn as much as he can from him. As Naruto grows, he might start to have his own ideas which could sometimes clash with Itachi's. But through communication and understanding, their relationship would become deeper. Itachi would share his past experiences with Naruto, which would make Naruto understand the complexity of the ninja world better, and in return, Naruto's innocent and determined nature would slowly change Itachi, making him more hopeful about the future of the ninja world.