Alien vikings would be awesome.
hmm, a story revolving around giant tree people with a 60 ft redwood as the main character
Everything has been done before. It's the curse we in the 21st century have to live with.
Everything has been done, even alien vikings:
Space Viking - Wikipedia, the free encyclopedia
Further proof that everything has been done:
The Adventures of Buckaroo Banzai Across the 8th Dimension - Wikipedia, the free encyclopedia
It's so surprising the first time you find out that your crazy, one-of-a-kind idea has already been done, most likely by some coked up guy in the 80s.
Still, good luck.
All glory to Haruhi! The one and true God!
Mind f*cked beyond repair
Instead of themes why don't you focus on new prespectives. That is something that can always be fresh.
Hi there, I'm into writing as well, so I'm sort of on the same page as you. In reality you can't be entirely original, everything can be related to something, good writing and stories comes more from execution and characters. To reach success you must challenge the readers by using interesting content (that already exists) but combining it with new and exciting ideas. Just think of something that you would like to read and write it, thats what I do and my friends seem to find what I produce very entertaining; more due great characters and unpredictable situations, yet I still get comments like (Oh like from that show etc etc)