One possible plotline could be that Amy feels neglected by Sonic's constant heroics and in a moment of weakness, she gets involved with another character. Maybe she meets a new character who shows her more attention and she starts to develop feelings for them, leading to her cheating on Sonic.
Perhaps in the 'amy cheats on sonic fanfic', it could be that Sonic has been acting differently, like being too overprotective or not understanding Amy's own growth as a character. This causes a rift between them and Amy ends up finding comfort in someone else, thus cheating on Sonic.
Some fans might be very shocked and disappointed. Sonic and Amy have a long - established relationship in the Sonic franchise, and this would be a huge deviation from what they expect.
For Amy, she could become more understanding of the 'evil' or opposing side. Instead of just seeing Metal Sonic as a bad guy, she might learn to look deeper into his existence as a creation. This could make her more empathetic in general.
Perhaps in the fanfic, there could be a power - based reason for Rias to 'cheat' on Issei. For example, she might need to form an alliance with another character, and as part of that alliance, she has to engage in actions that seem unfaithful. It could also be a test of Issei's loyalty. The author might be writing it so that Rias is trying to see how much Issei truly loves her by making him think she's cheating. Another idea is that there's a curse involved that makes her act out of character and towards other characters in a way that looks like cheating.
It could also be that Amy is so shocked at seeing Sonic hurt that she freezes for a moment. But then she pulls herself together and uses her own unique abilities, like her tarot card reading skills (if that's part of the fanfic's lore) to figure out what needs to be done to save Sonic.
In some plotlines, it could be a matter of self - discovery for Cas. He might think that his relationship with Dean is too constricting or that he needs to explore other aspects of love and connection. So, he cheats on Dean. However, this often leads to a lot of drama, with Dean finding out, and then there are a series of events like arguments, reconciliations, or even the end of their relationship depending on how the writer wants to take the story.
Another possibility is that she is protective of her relationship with Sonic. Fanfic might introduce elements that she feels are inappropriate or could potentially damage the 'purity' of what she has with Sonic. It's like she wants to safeguard the special bond they share in the official narrative from being sullied by unapproved fan - created stories.
Many fans might be shocked. Since Sonic is a well - known and family - friendly character, this kind of fanfic goes against the general perception of the character. Some might also be disgusted as it's a very unorthodox and inappropriate scenario for the Sonic universe.
Well, it might show Sasuke being put in compromising situations by Kabuto's schemes. For example, Kabuto could use his medical ninjutsu knowledge to create illusions that mislead Naruto into believing Sasuke is unfaithful. The plot could then revolve around Naruto's reaction and how he tries to uncover the truth.
One possible plotline could be that Bella suspects Edward of cheating. This might lead to a lot of tension between them. She could start spying on him, following his every move, which is very different from their usual relationship in the original story.
Well, in this kind of fanfiction, it could be that the cheating leads to a big confrontation between Damon and Bella. Bella might be heartbroken and decide to cut off all ties with Damon immediately. Then there could be a sub - plot where Damon's friends find out about what he did and they either support his bad behavior or try to convince him to make things right with Bella.