i did not understand the theme

You can make a game about the end of the world, being  at the end of the line not having any options or needing to end something ? hope that helps. 

You are given permission and frankly the recommendation to decide for yourself what the two words "The End" means. MR Ying had some great ideas, and you are welcome to use them as well as any other interpretations. As such, the world is yours. Power of creativity is in your hands. Make it happen! :)