So, Wattpad is a great site from where you can read a lot of books by authors that are just learning to write or are experts. Seeing that you want some good BTS fanfictions, here are a few good ones that I'd suggest which I've read myself too. I hope they'll help you for your assignment.
June - BTS Jimin Fanfiction
Interwoven - BTS Jimin Fanfiction
Carousel - BTS Suga Fanfiction
Repose - BTS J-hope Fanfiction
Love Agent - BTS Jungkook Fanfiction
Queen - BTS V Fanfiction
Mafia - BTS Jimin Fanfiction
Lucifer - BTS V Fanfiction
Worst Guardian Angel Ever - BTS V Fanfiction
My Demon Babysitter - BTS Jimin Fanfiction.
All these books are available in Wattpad. You can just search them up.