Multi-Verse

While this came off as similar to Space Opera (due to the content) I feel it can apply even to stories that take place on earth.  In Steins;Gate, Okabe and Daru create a cell-phone, microwave time machine.  At first no one believes him, and he doesn't believe it himself.  But then when he sees his phone has texts messages from the future, warning him of Kurisu's death...and he sees the death himself, he realizes that he time traveled.  The story continues, the experiments increase, and they get noticed by the government.  Time and time again he travels between different "world lines", searching for a universe where no one dies. 

The idea that there are other world lines is both interesting and terrifying to me.