Yuki, the main character, is an incredibly naive boy who is quick to forgive people. This major character flaw is played out beautifully against him. While at times it got frustrating to watch, it is also what makes him somewhat of a redeemable character.
Yuno is a mentally unstable girl who is completely obsessed with Yuki and from this emerges a complex and engaging character. Her draw isn't that she is likable. Her draw is her unpredictability and the way her crumbling mental state is played out through the series.
Her relationship with Yuki is a far cry from the tame romantic subplots that one encounters in most anime (and in most story telling mediums in general). At its best it's vaguely disturbing. At its very worst, it's downright horrifying. The author does not shy away from the gory details. I often found myself incredibly uncomfortable with the sexual components of their relationship. At the same time, it was a very fascinating dynamic to watch and the main reason I enjoyed the series.
That said, there are a few problems I have with this anime
-There were a few incohesive plot elements.
-Some of the character development felt forced. In particular, I felt that Yuki's character development was rather abrupt near the end of the series.
-There is fan service where there there really should not be fan service. The sexualization of 14 year old Yuno made me uncomfortable, particularly when you consider her mental instability.
I would also like to mention that there are a lot of potential triggers. Violence, rape, child abuse, and suicide are all reoccurring elements of the series. I would be cautious watching Mirai Nikki if you have trouble with any of these things.
