It All Started That Day (Attack on Titan x R...
Um...... not... check?
Yes, yes. Horrible description, I know. I'm not good with descriptions. Like at all. Fair warning, this is following the manga entirely. Sorry if you haven't read it. Or, you could look it up online (that's what I did and it updates when ever a new volume comes out) and read that chapter of the manga before reading the chapter I wrote. Just a suggestion.