The Future Diary: Episode 13

Ok, I am lost. I don’t understand how we have gotten to this point at all. I need some flashback to explain how events have built up to get to this point, cause I feel like I have missed something. Or multiple somethings to be honest. We have gone from Yuki and Yuno going off to watch stars while being chased, and Yuno not telling Yuki about this. To Yuki being locked up in some building and Yuno sitting on a chair with skulls setting traps?

I just don’t understand how we have gotten to this point. Or why Yuno would do things like this to Yuki who she is totally yandere for.