its becoming pretty clear the whole sister plotline was just a hook the editor had added in to make the story stand out
...and the real story the author wanted to write was this meandering slice of life slop
I'd be fine with that if "my sister who raised me in absence of our parents worked herself to death while shielding me from the cruel realities of our life, and this is the only connection I have to the side of her I never got to see" wasn't so fucking dire and dramatic a hook. Like, if you want to sucker in readers with an interesting premise, then flip it into lighthearted romcom, that's fine, but maybe pick something less tragic that people would actually like to learn more about.
Kind of reminds me of Super Cub, which is 99% a manga about cute girls riding motor cycles, sponsored by Honda, but also has this tragic premise of the heroine getting outright abandoned by her mother, and it's almost never brought up.