There will be a full background in it. But my plot idea is this:
Your life was normal, as much as it could be. Then your school was attacked by strange greyish monsters. One is about to kill you, when it's blasted away by a strange light. You come face to face with three children, each referring to themselves as a number. One in particular, XVI, destroys the grey creatures that are covering your school. As suddenly as it happens, it's over, like it never happened. Everybody forgot when the odd light faded.
But you didn't. And unfortunately it's going to come back to bite you, with the unusual virtual pet you got in the mail. What will you do with it?