Mirai Nikki OVA (2010) Not an OVA but a trailer with an extended time preparing you for what is coming. I think it is actually pretty great considering the animation is spot on and also the storyline is explained pretty well too. It serves as a great way to decide if you really want to watch the show and to be honest shows to me that you should definitely not let young children watch the show. I get that it is R17+ but when has that stopped anyone before. Honestly, give it a watch BEFORE the main series as a great insight. If you watch itafter then it may be a little bit lacklustre.

For those that slate it as not an OVA please remember this came out prior to the main release.