[Opinions] Re: I don't think Osono is a japanese first name ...
actually, I have no idea, sono is written in Katakana and therefore has no apparent meaning. Words written in Katakana are often of foreign origin, so I'm not sure where the name could be taken from, maybe from "Sonora". "sono" in hiragana usually means "that", but this one isn't really used for names.
As said, the "O" is part of the respect, which is never used in a name, would be way too arrogant and Osono-san would never refer to herself in that way, it's only others that call her like that respectfully. And usually one only adds "-san" to names, but not the "O" at the beginning, which is used for normal words like "O-sushi", "O-bento", that's what makes me think that it's some kind of title.
As first names f.ex. "Sono", "Sonoka", "Sonimi", "Sonoe", "Sonoko" exist and they can be written with the character for "garden, park". And Osono could be used as some kind of nickname for these. I sure there are some children that have been named after the character from the movie, dropping the respect.