Ok, I'll bite. I'm parrotting Woolymammoth a little, but this bears repeating.
There seems to be a huge amount of misinformation in online writing circles concerning the terms "plagiarism", "copyright" and "trademark". The names, characters and lands of TES are trademarks of Bethesda, and they own the copyright to the plots of their games. Thus if you take their characters/world/plot without their permission and use them to make a profit, you are violating their copyright and they may very legitimately sue you.
"Plagiarism" is taking someone else's words and either directly lifting or noticeably paraphrasing them, and claiming it is
all your own work. It is not the same as violating copyright. I am so, so tired of people trotting out the "fanfiction is plagiarism!!" attack on fan-works (not that you are, I just see it a lot). You would only be plagiarising Bethesda if you created a land called Tamriel and lifted the text of
The Real Barenziah word-for-word claiming you definitely, positively thought it up on your own.
Generally, companies turn a blind eye to fanworks, fanfiction included. It helps build a devoted and community-minded fan base, and it's never a good idea to alienate the people who love your games/books/movies/whatever by forbidding them to play in your world. In the vast majority of cases you would only be subjected to legal scrutiny if you attempted to make a profit from someone else's trademarked characters/world/plot. Therefore, turning in a piece of fanfiction as an English assignment is nothing to worry about, as long as - and this is very important - you indicated
exactly which parts are yours and which are Bethesda's. There shouldn't really be any need to name individual developers because there is no way to sort out who wrote what, but something like this would probably suffice:
"The world of Tamriel, its concepts and characters [excluding by name any that are created by you yourself] are copyrighted to Bethesda Softworks and Zenimax Media Inc. No profit it being made from this text and no copyright infringement is intended."
Edit: Talaran beat me to it