It could be Orochimaru. Since he has always been interested in obtaining powerful abilities, he might see Naruto with the Sharingan as a threat and try to take it for himself.
Danzo could also be a main antagonist. He was always power - hungry and paranoid. Naruto having the Sharingan might make him feel that Naruto is becoming too powerful and unpredictable. So, he could try to eliminate Naruto or control him. Plus, Danzo has a history of using underhanded means to achieve his goals, and Naruto's new power would be a great target for his schemes.
Another possible antagonist could be a rogue Uchiha who is jealous that Naruto, an outsider, has gained the Sharingan. This Uchiha might feel that the Sharingan is a sacred power of their clan and should not be in the hands of someone who is not an Uchiha. So, they would try to take it back by any means necessary, even if it means fighting Naruto and his friends.
Chapter 452, "Party of Four", is the clearest early answer because it turns Jiang Li's situation into a concrete plot event. Early on, Shang Shuyue glared at Jiang Yan, struggling to find the words to say.. By the end, Who could blame her when Jiang Li cooked even better than her mom?.
Chapter 415, "No Food, But Your Life", is the clearest early answer because it turns Tong Xiaoqi's situation into a concrete plot event. Early on, Are you begging me for food now?. By the end, Isn't the food and drink on the cruise much better than here?" Seeing....
Chapter 387, "Hello everyone, this is my disciple", is the clearest early answer because a shaky connection becomes usable in the plot. It opens with Liu Suqing V: "Even if we meet, I wouldn't recognize, faces covered...
Chapter 525, "Help It Transcend", is the clearest early answer because it turns Zhao Lang's situation into a concrete plot event. Early on, The forest at night was still quite damp and cold.. By the end, Not far away, a large expanse of deep red blood trailed across the....
Chapter 358, "That dress of hers must be a fake!", is the clearest early answer because it turns Jiang Li's situation into a concrete plot event. The chapter turns that into something concrete by moving from I just drove here slowly." In an instant, all cameras swiveled in his...
Chapter 359, "You Know Who I Am and You Dare Speak to Me Like This?!", is the clearest early answer because it turns Jiang Li's situation into a concrete plot event. It opens with Why do I hear a scream?" "This is...
Chapter 676, "Third Uncle Will Buy It for You!", is the clearest early answer because it turns Lin Manru's situation into a concrete plot event. The chapter gives readers a real answer by opening on Jiang Zhao Yuan felt somewhat embarrassed by such a direct revelation.
Chapter 444, "Wait and See", is the clearest early answer because it turns Yu Li's situation into a concrete plot event. The chapter gives readers a real answer by opening on Carrying a backpack, Yu Li walked for over ten minutes but ultimately...
Chapter 615, "River·Doraemon·Li", is the clearest early answer because it turns Shang Shuyue's situation into a concrete plot event. It opens with Everyone huddled close with their bowls in hand. and closes on This wind turbine is what I exchanged for yesterday..
Chapter 704, "Even if I were a slave, I would be willing!", is the clearest early answer because it turns Jiang Li's situation into a concrete plot event. The chapter turns that into something concrete by moving from Wu Daoshan looked at Zhao Lang in shock.