Hello from 6 Years in the future!So I think what happened is this: Kuniko and Mihoko lived together decades ago. Not sure of specific date but with the old TV it was probably the 80s. Kuniko's family set up an arranged marriage with a guy. Kuniko killed herself rather than marry someone who isn't Mihoko. The woman at the end is Mihoko reincarnated; the tragedy is that Mihoko could not live without Kuniko and also killed herself. That's why she doesn't know who Kuniko is, but feels nostalgic for her. Its also why she looks different and younger in spite of it clearly being a couple decades later based on the TV.
I've seen others criticize it as contrived or melodramatic that Kuniko killed herself instead of marrying a guy, since she could have refused and stayed with Mihoko. But being a lesbian in the 80s in Japan was extremely difficult. There was a lot of homophobia, and it mixed with sexism in some really awful ways. For example it was really hard for a woman to build a career in those days because it was expected that men had careers, while women quit the workforce as soon as she married. Mihoko was only barely able to support them when she's young, and it would get harder as she got older. And there would be a constant risk of them being outed and Mihoko losing her job. Also its not easy to refuse your family when you know that doing so may result in them cutting you out from their lives. That doesn't mean happiness as a lesbian was impossible; plenty of gay couples survived the homophobia of the 1900s. But I can understand how she might have a moment of weakness given the pressure she must have been feeling from society.
That said, I think I would have preferred a less miserable ending. Perhaps instead have Mihoko walk in as Kuniko is attempting to kill herself, so she can intervene and save her. Then maybe have Kuniko admit the arranged marriage. Mihoko then could ask her to run away together instead of marrying the guy. Maybe have a last page that shows them in a different run down apartment, poor but together and happy. Unfortunately that isn't how the author wrote it, but I would like to think that Mihoko reincarnating means Kuniko did as well, and that they will reconnect, this time in a time period which is more supportive.