Wow! I actually haven't finished Nana, my library had the first four volumes so that is what I read and then I learned it was unfinished and I was like welp no point getting invested now. But maybe now that I know it cuts off in a way that feels like an ending I will actually get around to reading the whole thing... Eventually... I'll try...
Have you read any of Yazawa's other work? It sounds like Nana gets a lot darker than Neighborhood Story or ParaKiss. I haven't read ParaKiss yet so IDK about that one, but in Neighborhood Story there's a recurring joke of the main character and her girl best friend being mistaken for lesbians until the main character starts dating her love interest. So Yazawa seems to know lesbians exist but like. I'm not sure how serious she is about it. It would be cool if the queer subtext was intentional but even if it wasn't death of the author is valid