Well, one of the most interesting plot twists could be a character that was thought to be on the side of the humans actually being a secret agent for the Titans all along. This would completely change the dynamic of the story and the relationships between the characters.
In this fanfiction, a possible plot twist could be that the power to turn into Titans is not a curse but a gift given to humans long ago by an ancient civilization for a specific purpose. This would turn the whole concept of the Titans on its head. It could lead to the characters re - evaluating their fight against the Titans and question whether they should be trying to eradicate them or find a way to co - exist.
Well, perhaps a major plot twist could be that the CCG (Commission of Counter Ghoul), which is supposed to be against ghouls, has been secretly working with some ghouls for their own ulterior motives. This would be a huge shock as it goes against everything they are known for. Also, there could be a twist where a ghoul's kagune (their weapon - like organ) mutates in a way that gives them an unexpected advantage or disadvantage.
One exciting plot twist could be Ben using his alien forms in unexpected ways within the Attack on Titan world. For example, using Heatblast to melt through the Titans' hard exteriors in a crucial battle. Another could be a character from Attack on Titan getting the Omnitrix and having to learn how to use it. This would completely change the power dynamics in the story.
Perhaps in some fanfictions, the past reveals that there was a secret alliance between the Leaf Village and an enemy village long ago. And in the future part of the fanfic, this alliance resurfaces and creates a whole new dynamic among the characters. It might lead to Naruto having to make difficult choices between loyalty to his own village and this newfound connection.
Well, a great plot twist could be that the Scarlet Witch in the fanfiction has a completely different origin story related to the Multiverse. Maybe she discovers that her powers were not a result of the Mind Stone experiments but something much more sinister from another universe. This would change her relationship with the Avengers and how they view her powers.
One possible intriguing storyline could be the characters from Attack on Titan somehow ending up in the One Piece world. For example, Eren could use his Titan powers in the middle of the Grand Line, causing chaos among the pirates and marines alike. Another idea is that the Straw Hat crew might find themselves in the walls of Paradis Island and have to deal with the Titans while also trying to find a way back to their own world. Maybe Luffy would try to befriend some of the Survey Corps members, like he does with most people he meets.
It could involve the characters seeing visions of a future where the Titans are finally eradicated. Maybe they see a world where humanity has rebuilt and is living in peace without the constant threat of Titans. For example, Eren might see a future where his friends are alive and happy, and this could change his actions in the present timeline.
A cool plot twist could be a ghoul - Titan hybrid. Imagine a Titan with the regenerative abilities of a ghoul. This would pose a whole new level of threat to the characters from both universes. Also, the idea of the ghouls' coffee being a valuable resource in the Attack on Titan world could be an interesting twist. Since coffee is so important to ghouls, it could have some unforeseen effects on the Titans or the people in that world.
Perhaps the character is reborn with memories of a future event that threatens the Mikaelsons. This would put them in a position to either try to change the future or use it to their advantage within the family dynamics. They might face disbelief from the Mikaelsons at first, but as events start to unfold as they remembered, they gain more influence.
One possible plot twist could be how his relationships change. For example, his friends might react with shock and confusion at first. Mikasa might have a whole new set of emotions to deal with, like a different kind of protectiveness. Also, the military might view him differently. They could be hesitant to send a 'female - Eren' into battle at first, or they might use his new form to their advantage in different ways, like using his appearance to deceive the Titans.
Mostly, yes. Fanfiction is a fan - driven activity. For Attack on Titan, the fanfiction community is quite large. The legality lies in the fact that it's not a direct replacement for the official work and is more of an addition. It's a way for fans to explore different scenarios and relationships within the Attack on Titan universe. As long as it stays within the boundaries of fair use, which it usually does in the case of fan - made stories, it's legal to watch or read.