yeah, I agree that it is the norm in Japan, to have only one job till the rest of your life, or staying in one company till the end. It's not my generation culture, idk about my parents. Millenials in my country changes job fast too, we indeed need money, and changing companies are usually the fastest way to get promotion etc lol.
Me saying like sumire does not have backups is because of that, like she can't change jobs because what she is doing right now is what she will be doing for the rest of her life (almost all professional jobs are like that right?). Like she can't suddenly do office jobs or change jobs, it's kinda scary like to depend your livelihood on only one thing, but that's just my thought, sumire is passionate after all, I am a person with barely any passion, so I could not relate to that haha. Tho most manga characters are passionate, which made their story interesting to read.