One common plot device is the 'accidental discovery'. For example, the protagonist might accidentally stumble upon a hidden vampire lair or a secret about a character's past. Another is the 'accidental transformation', like a human accidentally being turned into a vampire or a werewolf in an unexpected way. Also, the 'accidental meeting' of two important characters who were not supposed to cross paths can lead to a whole new set of events in the fanfiction.
Often in these fanfictions, a plot device is the existence of an alternate dimension. The Avengers could find a way to access this dimension where things didn't go wrong and bring back the good elements from there to fix their own world. Additionally, a Deus ex Machina - like event, such as a sudden, unexplained cosmic force that restores everything to normal, is sometimes used. However, this can be a less satisfying device as it doesn't really involve the characters' efforts as much. Another plot device is the power of teamwork being magnified to an extreme degree. The Avengers, by working together in a more perfect way than in the original story, are able to fix all the problems.
A typical plot device is the discovery of rare Pokemon. In these fanfictions, the main character might stumble upon a very rare Pokemon, and this encounter could attract other characters or Pokemon, gradually forming the harem. Also, the mystery element, such as an unknown power or a hidden place related to Pokemon, can bring the harem members together as they explore and solve it. And of course, the training montages where the trainer helps the Pokemon in the harem grow stronger are quite common too.
Often, there's the use of miscommunication. The kidnapper may have a wrong idea about the love interest that led to the kidnapping. For instance, thinking the person loves them when they really don't. Also, the setting can be a plot device. If the kidnapping takes place in a remote, mysterious location, it adds to the suspense and the sense of danger.
One common plot device is the 'what - if' scenario. For example, what if Hermione had been the one to save Harry from the Dementors instead of his father's Patronus? This can lead to a deeper emotional connection between them. Another is the 'arranged - relationship' plot, where they are forced to pretend to be in a relationship for some magical reason, but end up falling in love for real. Also, the 'jealousy' plot device, where they get jealous of each other's relationships with other characters and realize their true feelings.
A typical plot device could be the influence of an outside force. Say, a kind wizard or witch comes to the Dursleys and makes them understand the importance of Harry and his magic, and then they start to love him. Also, it could be that Harry himself shows extraordinary kindness towards the Dursleys in a difficult situation, which melts their cold hearts and changes their attitude towards him.
One common plot device could be the use of a powerful artifact or spell that enables the mind control over Ash. Another might be the presence of a villainous character who has the ability to manipulate Ash's mind for their own evil purposes, like to make Ash do their bidding or betray his friends.
Well, often there might be a plot device where Apollo gets jealous easily. So, if Percy shows any attention to other characters, Apollo would react in a possessive way. This could lead to conflicts between Apollo and those other characters. Also, the fanfiction might use the device of Apollo secretly following Percy around to keep tabs on him. He could be using his godly abilities to spy on Percy, which would add an element of mystery and drama to the story.
A plot device could be Cedric getting involved in Harry's personal quests. For instance, if Harry is trying to figure out something about his parents, Cedric may insert himself into the situation, believing he can protect Harry better that way. He might also try to monopolize Harry's time for training or studying, which could lead to some tension between them as Harry might feel smothered.
A third common plot device is the idea of redemption. Hades may be seen as a 'villain' at first for kidnapping Persephone, but as the story progresses, he tries to make amends. He could show her kindness, protect her from other underworld threats, and in doing so, Persephone begins to see him in a different light. This allows for a more in - depth exploration of their characters and their relationship.
One common plot device is the use of mind control or dark magic spells on Hermione. This forces her into the slave role. Another is the idea of Bellatrix using Hermione to get to Harry or the other members of the Order. Sometimes, there's a focus on Hermione's inner strength as she tries to break free from the slavery, which is also a plot device to create tension and drama.