His friends would be the most affected. People like Sakura and Kakashi who know Naruto well. Sakura is used to Naruto's kind - hearted and determined self. If he starts acting like Grimmjow, she'd be very confused and worried.
Definitely his friends and the people of Konoha. Naruto is like a ray of hope for Konoha. His friends such as Shikamaru, who have grown up with him and rely on his positive attitude. If Naruto starts acting like Grimmjow, his impulsiveness and aggressive nature could put them in danger during missions. And the younger generation of ninjas who look up to Naruto would be confused. They might start to question whether they should follow Naruto's new example or stick to the old Naruto's values. This could cause a lot of chaos and self - doubt within the Konoha ninja community.
One possible plot could be that Naruto, after being exposed to some strange chakra or magic, starts to take on Grimmjow's aggressive and fearless attitude. He might become more impulsive in battle, like Grimmjow, and start to challenge his enemies without much thought for strategy at first. His friends would be confused by this sudden change in his behavior.
Other Hogwarts students would be affected too. Those from non - pureblood families might start to fear or resent Harry. And the pureblood students like the other Slytherins might either welcome Harry into their exclusive circle or be suspicious of his sudden change. The teachers at Hogwarts would also have to deal with this new Harry, and some might be disappointed in his transformation.
His friends would be the most affected. For instance, Shikamaru, who is used to Naruto's normal self, would have to adjust to this new and somewhat spooky Naruto. He might have to come up with new strategies to deal with Naruto's new abilities and behavior.
In a 'naruto acts like gin fanfiction', Naruto might be quieter and more observant. Instead of his usual boisterous self, he could be more like Gin, who is often sly and calculating. Maybe he would have a more subdued way of showing his power and a different approach to his enemies.
The Akatsuki would be highly affected. Since Naruto has future knowledge, he could stop their plans before they even start. Also, his friends like Sasuke would be affected as Naruto could prevent Sasuke from going down the wrong path.
Sasuke would be one of the most affected. He and Naruto had a complex relationship, from being rivals to friends. Naruto's death would leave a huge void in Sasuke's life. Also, Hinata. She loves Naruto deeply, and losing him would be devastating for her.
Grimmjow's high - speed movement would be a great asset in the Naruto world. He could outpace many ninjas. His reiatsu - based attacks could be seen as a new form of energy - based jutsu. For example, his Cero could be like a super - powered ninjutsu blast. His ability to regenerate quickly would also give him an edge in battles against ninjas who don't have such a power.
His close friends like Sasuke and Sakura would likely be among the most affected. They know Naruto well and seeing him in a terrifying state would be very shocking for them. For Sasuke, who has a deep bond with Naruto, it would be especially hard to face a scary Naruto.
Sakura would be worried sick. She'd try to figure out what happened to Naruto to make him act this way. She might try to talk to him, use her medical ninjutsu to check if he's under some kind of genjutsu or has some other problem. She'd be very vocal about her concerns and would try to get the other villagers to help bring Naruto back to his normal self.
I think Sango would also be greatly affected. As a female in the group, she might feel a stronger sense of responsibility towards baby Kagome. She would be worried about how to take care of her properly, especially in their rather dangerous world full of demons. And she might also be concerned about how this would impact their overall mission and group dynamic.