The above description basically fits Mirai Nikki to a T if you accept Yuno as the protagonist (protagonist!Yuki is completely static and thus a boring protagonist so we reject that out of hand). Our heroine Yuno, is an orphan, like so many other classic protagonists. At the start of the timeline, she is thrust into a situation where her foster parents abuse her either through neglect or physical/mental cruelty. After Yuno pushes against the stifling status quo by accidentally murdering her parents, she spirals into a depression wherein she has nothing to live for. What is the point of life? What does it all mean? It is a chance encounter with Yuki that gives her the drive to keep on living, and much of the emotional driving force of the story results from her ever-changing relationship with Yuki.
As it turns out, Yuki and Yuno have quite the dysfunctional relationship due to their underlying psychological problems. Yuno, ultimately, wants to be loved. Raised as an orphan, she didn't have the luxury of a parent's embrace when she was feeling down or lonely. Her foster parents were barely any better; her dad was never home and her mom, suffering from her own issues, foisted her unrealistic expectations onto Yuno - never praising her, always criticising. Yuki's random act of kindness, a product of his fumblingly genuine nature, initially enthralls Yuno precisely because it's a ray of warmth in Yuno's cold world. Latching onto this one positive snapshot in her life, Yukiteru quickly becomes an obsession for Yuno, the one thing that can keep her "happy," relatively speaking. Yuno says herself, "I would have fallen in love with anyone who let me cling to them! And you would have fallen in love with anyone who was willing to protect you."
Meanwhile Yuki's characterization boils down to dumb milquetoast guy with an Oedipus complex. Oh, and he's scared of everyone. Obviously Yuno is more protagonist-like than Yuki from this alone.
Anyway, Yuki takes advantage of Yuno's generosity in an increasingly abusive relationship (Yuki admits that "It's true that I was using Yuno" in Episode 25), holding her back from realizing her real dream, which comes in two parts: 1) To let Yukiteru win the Survival Game and become god, and 2) To die so that her suffering may end. Yuki cruelly rejects Yuno's desires multiple times, forcing her to take matters into her own hands. In fact, it isn't until Yuno makes the ultimate sacrifice, by killing herself, that she finally realizes her wish and all the plot lines are resolved with happy ends everywhere. Meanwhile, all Yuki does is get in the way. You know what we call someone who gets in the way of the protagonist's goals? That's right, Yuki is the antagonist.
...
I just remembered the dream I had this morning...
The dream?
Uh-huh, it was really weird. I was playing a survival game, with diaries that told the future.
Oh, that sounds interesting.
And in my dream, I fell in love with this peculiar girl.
A peculiar girl? I thought you preferred normal girls.
Why did you fall in love with her?
Well...
It's probably for the same reason that I love you two.
Because she was always there for me...
