The most popular is probably 'Sword Art Online: Progressive'. It has gained a lot of popularity due to its in - depth look at the early floors of Aincrad. Fans love how it expands on the original story and gives more backstory to the characters.
Well, 'OP' in the context of this 'Fury Tries to Kidnap OP Harry Potter Fanfiction' could be the main character that Fury is targeting because of their special powers. Maybe it's a new character created by the author with unique magical abilities that Fury, for some reason, wants to get his hands on. It could be someone with a combination of different magical skills from the original Harry Potter universe, like being able to perform extremely powerful spells without a wand or having the ability to control all types of magical creatures.