The Akatsuki could still be the main antagonists. Even with Naruto's training by the Kyuubi, they would be after the tailed beasts. Their goals of collecting all the tailed beasts would put them in direct conflict with Naruto. And they have some really powerful members like Pain and Itachi.
It could be some rogue shinobi who are jealous of Naruto's new - found power from being trained by the Kyuubi. They might form an alliance to take Naruto down. These shinobi could have their own motives, like seeking revenge on Konoha or wanting to use Naruto's power for themselves. They could be from other hidden villages or even some outcasts within Konoha.
Another possibility is that a new group emerges, one that is afraid of the power Naruto could gain from the Kyuubi's training. This group might see Naruto as a threat to the balance of power in the ninja world. They could be made up of some old - school ninja clans who believe in a more traditional way of power distribution and see Naruto's rapid growth as something that could disrupt their way of life.
If you want the clearest chapter reference, go to Chapter 37. Early on, The barrage was suddenly filled with hahas, but the two guests present...; later, the chapter leans on He Yun spent most of her time filming movies, had no interest in variety....
Chapter 884, "Master?!", is the clearest early answer because it turns Miss Jiang's situation into a concrete plot event. Early on, I've heard this temple is quite magical, but why are there so many.... By the end, After all, Master often goes on retreats, leaving the teaching to the....
Chapter 878, "Do You Dare?", is the clearest early answer because it turns Jiang Li's situation into a concrete plot event. The chapter gives readers a real answer by opening on Su Yinwan not only chose a remote location for the meeting, but the...
Chapter 891, "If You're a Man, Keep Drinking!", is the clearest early answer because it turns Jiang Zhao Yuan's situation into a concrete plot event. A useful checkpoint is the way the scene starts with Jiang Yan couldn't bother to coax these two little brats anymore.
If you want the clearest chapter reference, go to Chapter 53. Early on, Night had fallen over Chixia Village, eerily void of any human sounds.; later, the chapter leans on Jiang Li followed the village chief's wife down a narrow path leading to....
Look to Chapter 15 for the clearest answer. It begins with Jiang Shixu woke up from those nightmares filled with blood and darkness,..., keeps building through The two sleeping pills he took in the evening had left him with a..., and lands on Since she didn't move, Jiang Shixu also stayed put, and.
Look to Chapter 61 for the clearest answer. It begins with Hahahaha, oh my god, Jiang Li's mouth is even more venomous., keeps building through She broke Jiang Yan's defense with just one sentence." "Laughing to death,..., and lands on A cold shower is pretty normal, right?.
The best chapter pointer here is Chapter 33, "Variety Show of Villains". It opens with Following the announcement, five artists respectively reposted the Weibo—... and closes on Although Su Yinwan was considered half a goddess to him, the whole thing....
If you want the clearest chapter reference, go to Chapter 13. Early on, Sensing that something was off with Jiang Yan, Jiang Yan dismissed the...; later, the chapter leans on What on earth do you mean?" Ignoring him once again, Jiang Li shifted her....
Chapter 926, "Doomsday Beehive Exploded?!", is the clearest early answer because it turns Jiang Cheng's situation into a concrete plot event.