The fact that Hikaru left everything for Hana does doesn't really bother me. It happened too fast for sure, but it's not that far stretched from her portrayal since the beginning. Like wanted to quit her job, just so she can be sure to greet Hana when she arrives.
What bothers me the most is how Hana is portrayed. From the easy going, playful and manipulatrice girl, to a harmless little girl? That's weird. That doesn't match and worse, this is extremely infantilizing. As if she wasn't responsible for her actions, and she was only acting that way because of how she was treated before. Even with a longer development, I'm not sure I would have accepted that. The girl is 35, not a teenager anymore.
While we don't know if this was axed or not, at the end of the day, this is bad writing. The story didn't developed that much in volume 1. And there were lots of superfluous moment that could have been cut in volume 2 to allow for better development.
I would have preferred if both girls would have go their own way, as a mean for self discovery and reflection. That would have been less conclusive, sure, but it would have been possible to wrapped up the manga in a more logical way I think.