@lightningcloud You can rest easy, because this one is a little shorter. Well, there's also a sequel series, but Mai's Dad plays a much smaller role in that so it's quite different.
...is there going to be a big reveal that the mom actually died and the father acts like that to cover it up so the daughter won't be sad? I feel like that might be coming.
She's not dead, she sends them postcards and talks to Mai on the phone. She left them because she couldn't deal with her husband and Mai wouldn't leave him (most likely because she knew he could never make it on his own).
Sad, but staying unhappy just for the kids isn't always the right answer.
Obviously, the latest chapter definitely settles the question since the mother is actually present in person, but before that the only communications we had been shown were letters. If the mother had, in fact, died, then it would be easy to have her parents (Mai's grandparents) fake that kind of contact, either by just sending the letters directly or by sending them to a friend somewhere inconvenient to visit to be re-mailed.