OK, I guess
the ending was a bit mediocre to be honest. The viewer finds out why the mysterious girl died, thus explaining her ghost's presence, but the main character (the mother) just sort of disappears with the ghost without any clear explanation as to what she did. at the end, the daughter of the main character just sort of casually goes into the then-abandoned apartment building, sees her other appear, and talks to her like she's not an apparition that manifested itself. And when her mother's spectre disappears just as quickly, she still doesn't seem to care. Also, since this is a spoiler anyways, why wouldn't the mother have called the cops upon realizing that there had been a corpse in the apartment cistern for like 2 years?
as for subversive themes, there are none, so don't worry about that.
Overall, a bit mediocre when comparing to Japan's reputation for spooky s**t.
It was OK. Not better, not worse. The premise of the movie is decent, but I feel as though there are holes in it, and they could have done a lot better especially with the ending. It wasn't s**t-your-pants scary, but did have its moments. It doesn't rely on jump scares too much.