Kiriko's character was kinda odd

Obviously this wasn't the most realistic movie, but out of everything one thing that really bothered me was how Kiriko's character was written. Basically she was just a plot point to Raizo's backstory. Raizo's cheesy metaphorical heart, I suppose. I just found it really hard to believe she would turn out to be such a normal let alone sickeningly sweet girl having been raised in the same harsh environment as the rest of those kids.