At first, Sasuke might not believe it was Naruto's own will. He would try to find out if Naruto was under some sort of external influence. But if he found out that Naruto was fully responsible, Sasuke's reaction would be one of pure hatred. He would abandon all his previous beliefs and goals and make it his sole mission to destroy Naruto. He might also cut off all ties with the village that Naruto was protecting, seeing it as an accomplice in his sister's death.
The village of Konoha would be in chaos. Naruto was seen as a hero, and if his dark side kills Sasuke, it would shatter the trust of many. His friends like Sakura would be devastated. She might go on a revenge quest against Dark Naruto. The Uchiha clan, which Sasuke was part of, would also be in turmoil. They might see this as an act of aggression against their clan and seek justice.
At first, Sasuke would be filled with rage. His Sharingan was something he had cultivated and was a symbol of his Uchiha heritage. Naruto stealing it would be like stealing his very soul. He would immediately try to hunt Naruto down. But as he chases Naruto, he might start to think about the reasons why Naruto did it. He could consider if there was some greater threat that Naruto was trying to combat, but still, he would not be able to forgive Naruto easily and would demand his eyes back.
The village of Konoha would be in shock. Naruto is seen as a hero, but killing Sasuke, who was also a powerful and well - known ninja, would be a very controversial act. Some might support Naruto, believing he had no other choice for the greater good. Others would be angry and might even turn against him, thinking he could have found another way.
His other friends like Shikamaru would be in shock. Shikamaru, who is usually calm and collected, would struggle to come to terms with Naruto's death. They would all have to deal with the loss of the village's hero and a great friend, and it would likely change the dynamics of the entire group.
Some villagers might be shocked and horrified. Naruto has always been seen as a hero, and this act of killing the council would shatter that image for many. They would fear that Naruto has gone rogue and might pose a threat to them.
Sasuke's reaction could be complex. At first, he would be enraged. After all, the Rinnegan is a symbol of his power and his journey to gain strength. However, he might also have some mixed feelings. He and Naruto have a deep bond, and he might wonder if Naruto had a good reason for taking it. But overall, his initial reaction would likely be one of fury and a desire to get his power back.
If Naruto has a sister in the fanfiction, Sasuke might see her as another connection to Naruto. He could initially be suspicious of her, thinking she might be a liability to Naruto. But as time goes on, if she proves herself to be strong, Sasuke might respect her. Their relationship could also be a source of some jealousy for Sasuke, as Naruto might spend more time with his sister.
Naruto would be devastated. Sasuke is his closest friend and rival. He would likely go into a state of deep mourning at first. He might isolate himself for a while, just trying to come to terms with the loss.
Naruto would be devastated. He's always been one to value his friends deeply. He might initially go into denial and then be filled with rage, vowing to find out who or what was responsible for her death and seek justice. He would also likely carry a great deal of guilt, thinking that he should have been able to prevent it.
Naruto would probably be very confused at first. He trusts Sasuke, even if it's a Fem Sasuke in this fanfiction, and he wouldn't expect to be kidnapped by her. So, his initial reaction might be to try and talk to her, asking her why she's doing this.