Yes, there might be. The Naruto and Attack on Titan fandoms are both huge, and fans often like to cross over their favorite characters in fanfiction. So it's quite possible to find Eren - from Attack on Titan - in Naruto fanfiction. However, it may not be as common as fanfictions within each respective universe.
Well, the show 'Murders in the Building' claims to be based on a true story. It might draw from real - life crime investigations, like the way crimes are solved, the relationships between the suspects and the detectives, or the types of motives that drive people to commit murder. However, a lot of creative license is also used to make it more entertaining for the viewers. For example, the characters in the show are likely composites or exaggerated versions of real - life people, and the sequence of events may be rearranged for dramatic effect.
There could also be a group of villains working together to kidnap Sonic. For instance, a combination of Eggman and some of his more powerful robot creations along with a couple of other villains from Sonic's rogues gallery. They might have a grand plan that requires Sonic's capture, like using his power to open a portal to a world full of chaos energy that they can then control.
A jealous rival of Inuyasha might kidnap Kagome. For example, another demon who wants Inuyasha for himself might think that by taking Kagome, he can get Inuyasha to do his bidding. This would create a lot of drama and conflict between Inuyasha and the kidnapper.
The Grimm could also be involved in an unusual way. Perhaps a new type of Grimm that has the intelligence to kidnap. They might be working with a human or Faunus villain who has some sort of control over them, and they take the character to an unknown location where the RWBY team has to face not only the Grimm but also the mastermind behind it.
Often, in these fanfictions, Eren develops more empathy. He starts to really understand Mikasa's feelings. For example, he might realize how much his actions impact her and become more cautious. He becomes more of a protector instead of just a fighter.