For Naruto's relationship with his friends in general, it could be a turning point. If Sakura handles the situation well and supports Naruto, it could encourage the others to do the same. However, there could also be a bit of a rift if some friends are scared of the implications of him being a jinchuuriki. But overall, Naruto's own attitude towards his friends will also play a big role in how these relationships develop. He'll need to be open and reassuring to maintain those bonds.
Some of his other friends might react differently too. Some may be more cautious around him, worried about the power of the jinchuuriki within him. But those who truly trust Naruto, like Shikamaru, might not change their attitude much. They would see that Naruto is still the same person he was before, just with this added aspect to his identity.
Well, in this kind of fanfic situation, Sakura could also become more protective of Naruto. Since a jinchuuriki is in a rather dangerous position, she might start to see him as someone who needs her support more than ever. She could try to keep his secret safe from those who might want to harm him because of it.
She might be initially shocked. Sakura has always seen Naruto as a friend, so learning of his romantic feelings could completely change her perspective of him. It could make her re - evaluate all their past interactions.
Another development could be that Sakura starts to develop feelings for Naruto as she spends more time thinking about his love for her. She might notice things about him that she never paid attention to before, like his kindness and determination in a more romantic way.
For Merlin, there are both good and bad consequences. On the bad side, some of the more traditional and anti - magic people in Camelot might try to oppose him. However, since Arthur now knows, he has a powerful ally. Arthur can protect Merlin from those who would do him harm. Also, Merlin can now be more open about using his magic for the good of Camelot, which is a positive change.
One possible development is that Sasuke becomes more involved in the village. He realizes he needs to create a stable environment for his family, so he starts to take on more responsibilities in the village.
In a Sakura Cardcaptors fanfic where Chelsea finds out, she might react in different ways. She could be shocked and initially not believe what she has discovered. For example, if she finds out about Sakura's secret cardcaptor identity, she may question how such a thing could be possible in the seemingly ordinary world they live in.
The village of Konoha would be in mourning. Naruto was a hero to them. Kushina's grief could spread throughout the village, dampening the spirits of everyone. There might be a sense of hopelessness as Naruto was often seen as the one to bring hope in difficult times.
Fleur might expose them. If they are students, they could face expulsion from Hogwarts.
Well, one possibility is that Dark Naruto would be overjoyed. After all, Kushina is his mother. But at the same time, he could be very conflicted. His dark side might make him suspicious of her motives. He could test her in various ways to see if she's really who she says she is. And Kushina, on her part, would probably be heartbroken to see what her son has become.
In many fanfictions, it might start with Sakura noticing small things about Naruto that she hadn't paid much attention to before. For example, his unwavering determination in the face of difficulties. This newfound awareness gradually grows into admiration and then love as she spends more time with him, either on missions or during downtime in the village.