The whole lead-up suggested that she suffered something really terrible, and that was important to the story that was being told, but in the end it was just sort of blown off in favour of a pretty mild story about them meeting as kids, and acting pretty normal toward each other.
It seems like an attempt to raise the stakes, before ending anticlimacticly when it turns out there's no substance behind the dramatic foreshadowing. There was something similar in the last part of Cross Heart, where it starts out with Haru so depressed and on the verge of giving in to despair, but then it's revealed that Kotomi just hadn't spoken to her for a few weeks as some kind of petty revenge.
Wait, that's all we get of Haru's past that was so terrible that she blocked out everything before the age of 10? One panel of her parents arguing, and a couple references to how they fight all the time and say bad stuff?
There was probably more but for the sake of the story it focused on the relevant bit.
That's the problem, the story suggested that was the relevant bit, what with Kotomi being afraid that Haru remembering their meeting would also bring back the terrible trauma that must have happened to make her lock away a huge chunk of her childhood.
But then we got bait & switched, the terrible trauma was never revealed and the whole issue was blown off in the end.
It was said that her parents abandoned her. The scenes where her parents fight and the overall way they don't care for her are to show how it came to that. We aren't really shown how it happened, but that's where the magic of imagination saves the day. She could have been left at a relatives house or she could have been literally left alone somewhere... That seems pretty traumatic to me.
Also, I think the purpose of the whole "memories of the past" buit up was for the sake of the moment Haru cares more about the good memories than the bad ones. Even Kotomi was afraid Haru would "break," but she didn't. what's more, she cried her heart out and that's a good symphtom when it comes to healing emotions.
All in all, starting from Cross Heart, this story is more about showing how much they love each other than bringing a compeling mystery story or something... This is supposed to bring the fluffs~ (/°´°)/ ~ <3
(I have my own issues with their not so healthy dependancy to one another... I'd rather have more of a supporting couple that can stand as equals... I'm more of a "I want to be stronger for this persons's sake" than "I'm stronger because of this person" follower, but all in all I really enjoy AnaKriss work -v-)