One common scenario is when Sakura chooses Sasuke over Naruto time and time again. It makes Naruto feel like he's second best, which deeply wounds his heart as he loves her so much.
Another situation could be that Sakura lies to Naruto about her feelings. Maybe she pretends to have some level of romantic interest in him just to keep him around for her own needs, like protection or to make Sasuke jealous. When Naruto eventually finds out the truth, it would be a huge betrayal and would cause his heart a great deal of pain.
Often, in fanfictions, power struggles can lead to Boruto hurting Naruto. If Boruto becomes too power - hungry and Naruto tries to stop him from going down a wrong path, Boruto might see it as Naruto trying to keep him weak. This can lead to conflict between them. Also, there are times when Boruto blames Naruto for the death of someone close to him (even if it's not Naruto's fault), and in his anger, he hurts Naruto.
One common scenario is when Naruto is in a life - threatening battle. Sakura will be on the sidelines, worried sick and using her medical skills to the fullest to keep Naruto alive. She might even put herself in danger to reach Naruto if he's in a precarious position on the battlefield.
One common scenario is during battles. Naruto would be right by Sakura's side, deflecting attacks aimed at her. Another is when Sakura is facing emotional distress. Naruto would be there to comfort her and protect her from any further emotional harm.
In some fanfiction, Naruto might become disinterested in Sakura because of a change in his ninja career. For instance, if he is assigned to a long - term mission far away from the village where Sakura is. During this time, he meets new people and has new experiences that change his perspective. He could also start to value different qualities in a person. Maybe he used to like Sakura's determination, but now he realizes that there are other qualities like kindness and acceptance that are more important to him. And Sakura doesn't possess these new qualities he values, so he loses interest in her.
Often, in fanfiction, Katara can hurt Zuko's feelings by bringing up his past wrongdoings. She might do this in the heat of an argument, not realizing how much it still affects Zuko, who is trying to move past his old self. This can make Zuko feel like he'll never be fully accepted by her.
One common scenario is when Inuyasha is too stubborn to listen to Kagome. He might think he knows best all the time and not give her a chance to speak or contribute. This makes Kagome feel ignored and unimportant. For example, when they are discussing a strategy to fight a powerful enemy, Inuyasha just shuts her down without even considering her ideas.
Sometimes, in fanfiction, Sakura might use her medical skills against Naruto in a negative way. For example, if she withholds treatment or gives him a wrong diagnosis out of some conflicted feelings towards him. This is quite cruel and can cause both physical and emotional harm to Naruto.
Sometimes, in fanfiction, Greyback is sent by Voldemort to target Hermione specifically. He could physically harm her to send a message to the Order of the Phoenix. Or, in a scenario where the Ministry has fallen, Greyback might hunt Hermione down in the chaos, seeing her as an easy target because of her status as a Muggle - born.
One possible scenario could be that Vegeta is too focused on his training and ignores Bulma's emotional needs. He might be constantly pushing himself to get stronger and in the process, not give Bulma the attention she desires. For example, he could skip out on family events or important dates just to train.
One common scenario is during training sessions. Naruto's enthusiasm, Sasuke's determination, and Sakura's focus combine well. They push each other to improve their skills. Another is when they are on a mission together. Naruto might crack jokes to lighten the mood, Sasuke stays focused on the mission goals, and Sakura uses her medical skills and strategic thinking to keep them all in good shape. They learn to trust each other more in these situations.