Honestly, the story for Hero for 30sec (Yuusha 30) isn't as interesting as its unique gameplay and style, though you'll still want to watch this trailer (found after the break) to get a better understanding of the game. Hero for 30sec follows a war between humans, who are on the verge of extinction, and 51 demon kings. See, it's the result of a 500-year-long battle ... which you'll only get to play the final 30 seconds of.
Make sure you stick around and watch the whole vid (it reveals a new four-player ad hoc mode!), otherwise you might miss some hilarious-looking CG near the end.