It could be Orochimaru. He has always had an interest in Konoha and its secrets. Maybe he decides to launch a full - scale invasion this time to get his hands on something he desires.
Naruto is, of course, very memorable. His determination to protect the village against Pain is always a central and inspiring part of any such fanfiction.
Naruto could also be more focused. The experience of the Pain invasion made him realize the importance of being fully present and concentrated during battles and training. He might have less of his usual goofiness and be more serious about his growth as a shinobi.
Well, perhaps in this 'naruto invasion of konoha fanfiction', Naruto is actually being mind - controlled to lead the invasion himself. It would be a huge shock for his friends and allies when they find out. This could lead to a lot of internal conflict as they try to figure out how to stop him without hurting him.
A great plot twist might be that some of the villagers who were thought to be innocent are actually in cahoots with Pain. They could have been secretly helping him all along, providing information or weakening Konoha's defenses from the inside. This would shatter Naruto's perception of the village and add a lot of drama and conflict to the story as he has to deal with both external and internal enemies.
Their relationship could develop through shared trauma. During the Pain Invasion, they face a great threat together. This might make them rely on each other more and understand each other better. For instance, Naruto might see Ino's courage in the face of danger, and Ino could see Naruto's selfless nature up close.
The Konoha 12 would likely be in shock. They've seen Naruto grow, but this fight against Pain is on a whole new level. Some, like Shikamaru, would immediately start analyzing the battle strategies. Sakura might be worried sick about Naruto's safety, while Kiba could be cheering Naruto on loudly, impressed by his power.
In this fanfiction, Jiraiya and Pain are the main characters in the fight. But from Konoha's side, Naruto is a very important one. His emotions for Jiraiya would be running high. Then there's Sakura, who is not only a skilled medic - ninja but also cares about the safety of the village. She would be worried about the outcome. And don't forget about the elders in Konoha. Their opinions and reactions to the fight would also play a part in the overall story of this fanfiction.
Well, you can expect a lot of intense emotions. Konoha characters would be on the edge of their seats, seeing Jiraiya fight Pain. There might be shock at Jiraiya's skills and the power of Pain's attacks. They could also be filled with pride for Jiraiya or fear for his safety. And of course, there would be a lot of reactions to the twists and turns in the fight, like gasps when Jiraiya makes a risky move or when Pain reveals a new jutsu.