Now THIS feels like a perfect example of bad writing.
The entire time this event was going on I felt like the author decided this had to happen in order for Ouka to think it's ok to fall in love.
It never felt like she went there out of her own will, just that the author wanted her to be there for plot to happen (plot induced stupidity).
It was so abrupt that it completely took me out of the story.
I feel like If it was a joint school trip or something and she snuck out at night because she wanted to see the spot where her mom and dad met and wound up lost (and Arata was the only/first one to go look for her) that would have probably worked a lot better.
But with this I could almost physically see the hands of the author scooping the characters up and placing them here in order to get the story going.