I like Naruto in these fanfics because he always stays true to his beliefs. He is constantly trying to bring Sasuke back to the village and is willing to fight for their friendship.
He'd probably be very intrigued. Percy has a penchant for adventure and new things, and this fanfiction would be something completely different from what he's used to.
Sakura would be devastated. She has deep feelings for both Naruto and Sasuke. She might turn against Sasuke completely and try to take revenge herself. Kakashi would be in shock. He has mentored both and would likely feel like he failed in some way. As for the other ninja from the Hidden Leaf, they would be angry and mournful at the loss of their hero Naruto.
Naruto would probably be angry at first. He's always been a free - spirited person, and being kidnapped by Sasuke, his friend - turned - rival, would surely make him mad. He'd likely try to fight back immediately, using his ninja skills and his never - give - up attitude.
One of the best moments is when they have a rematch that showcases their growth. Naruto has become stronger with his new jutsu, and Sasuke has further mastered his Sharingan powers. The intense battle of ideologies during the fight is captivating.
Sasuke's reaction would be the most complex. He would be filled with guilt for causing Naruto's death. He would also feel a new sense of purpose, to live up to Naruto's sacrifice. Sasuke might become more withdrawn at first, dealing with the enormity of what has happened. The other ninja from Naruto's generation, like Shikamaru, would be sad but also respect Naruto's choice. They would support Sasuke in his new path, as they understand it was what Naruto wanted. And the younger generation would see Naruto as a martyr, someone who sacrificed for a greater good.
Sakura would be devastated. She has deep feelings for both Naruto and Sasuke. She would probably be angry at Sasuke for killing Naruto and at the same time feel guilty for not being able to stop it. She might even try to take revenge on Sasuke.
Obviously, Naruto and Sasuke are going to be the main characters. Their relationship and how it develops after their fight is likely to be the central focus of the fanfic.
Naruto himself would likely be outraged. He has his own goals and reasons for his relationship with Sasuke, and being labeled as a 'fan' by Ino would be offensive to his pride. He'd probably try to set the record straight right away.
Sakura would be completely devastated. She's been in love with Sasuke for so long and has a deep bond with Naruto too. She might go into a deep depression and lose her will to be a ninja for a while.