One common plot twist could be that Hinata finds out she was actually set up. Maybe someone was jealous of her relationship and made it look like her partner cheated. This would add a layer of mystery and give Hinata a chance to fight for her relationship.
Another plot twist is that the person who cheated has a really good reason. For example, they were trying to protect Hinata from something dangerous but went about it the wrong way. This would make Hinata have to decide if she can forgive based on the intention.
One common plot twist could be Natsu seeking revenge on the person who cheated on him.
One common reaction could be Naruto's shock. In most fanfictions, Naruto is portrayed as someone who deeply loves Hinata, so being cheated on would leave him completely stunned.
One plot twist could be that the person who cheated on Naruto actually has a very good reason, like they were forced to do it to protect Naruto from a greater threat. Another could be that in ANBU, Naruto discovers that the cheating incident was part of a larger conspiracy against him. Maybe his new ANBU teammates turn out to be related to the cheater in some way, creating a lot of internal conflict for Naruto.
Sometimes, the plot twist is that Stiles is actually in on the kidnapping in a way. Maybe he's trying to protect his friends from a greater danger by faking his own kidnapping. So all the while his friends are searching for him, he's actually on a secret mission of his own, which is revealed later in the story and makes for a really interesting read.
One common plot twist could be that a close friend or ally, who Ichigo thought he could trust completely, turns out to be working for the enemy all along. For example, Orihime might be brainwashed by a powerful Hollow to feed information about Ichigo's whereabouts and plans to the Hollows. Another could be that the Soul Society, which Ichigo has often helped, decides to turn on him due to some false accusations of him being too dangerous. Maybe they believe he is on the verge of losing control of his Hollow powers and decide to eliminate him before he becomes a threat to both the living world and the Soul Society.
One common plot twist could be that Aria survives the shot but loses her memory. This then leads to a whole new set of relationships and self - discovery as she tries to figure out who she is and who would want to harm her. Another could be that the person who shot her is someone she thought was a friend all along, creating a sense of betrayal and mystery.
One common plot twist could be that the kidnapper is someone Allen thought was a friend all along. It adds a sense of betrayal and shock to the story.
In some fanfictions, a plot twist could be that Haruhi's kidnapping is part of a virtual reality game that she unknowingly entered. The 'kidnappers' are just players in the game who are trying to win by capturing her. Another common plot twist is that the kidnapper has a change of heart halfway through. They start to see Haruhi's good qualities and instead of harming her, they end up helping her. And sometimes, it could be that the kidnapping is a test set by a mysterious organization to see if Haruhi is worthy of some special task or knowledge.
One common plot twist could be that the person she trusts most, like her best friend, betrays her for power. Maybe her friend is offered a high - ranking position in a magical guild or something and has to sacrifice Lucy to get it. Another could be that a love interest betrays her. He might be secretly working for an enemy and using Lucy to get information about her family or her magic.
Hinata might react with anger. She's a strong - willed character deep down. So she could confront the person who cheated on her head - on. She might yell and express her disappointment and hurt. This would show her growth from a shy girl to someone who stands up for herself.