Thanks for listening, friends.
I think, this is one of these stories that can touch many people who experienced loss on many different levels.
Such personal loss is not limited to death... but can linger and impact us just as much.
Sharing these stories may not be directly refering to the manga in question, but I hope the mods agree that it's still on-topic, when we talk about our experiences - relating to the manga, premise and characters...
I'm going to say that they probably just fell out of touch. It could be as simple as that. Tsugumi's dialogue gives off hints that she has a fondness for Midori (which makes this story just so much sadder to read), but obviously this was never explored and probably just left alone.
Yeah, I wonder... They seemed mutually close. Tsugumi was popular and had had other 'associates'. How old where they during these flashbacks? Middle School / Junior High School spans from 12/13 to 15/16?
Tsugumi had Haru when she was 17, so she got pregnant only a few months after graduation.... (There's a slim chance she got pregnant during school, too. But I don't know the exact school-enrollment age-range/-tolerance.)
I get the sense the implication is, that Tsugumi and Midori were close until graduation, at least.
I dunno, I know that them girls easily fall apart after graduation, going to different schools or just because life happens. But somehow it sticks out to me how Tsugumi still saved Midori's contact but they never so much as spoke again - and how Midori knew she'd never see Tsugumi after graduation ever again.
Yet Midori impacted Tsugumi so much she seemed to have talked a lot about her to her daughter... So much Haru recognized her without being introduced!
There seems to be a lot of family issues going on for Tsugumi; (the no bento might be important foreshadowing,) running away, teen-pregnancy, disinherantance, divorce... no friends, and her parents didn't come to her funeral and nobody but the aunt cared for Haru - and even the aunt seemed easily convinced to hand Haru off to what's basically a total stranger, possibly implying that while she's one of the nicer or at least more responsible people, she didn't have much contact with Tsugumi and the child either, lacking a personal connection (having kids of her own, if a relative was raised alonggside them, one may feel much more responsible and attached to them - even if that means to take care for an additional kid).
I wonder, if Tsugumi's life-story won't turn out to be even more sad and hurtful than her passing away and the resulting loss we see the characters now going through...
(Not sure how much of that may have rubbed off on Haru; Tsugumi as a working-mother still seemed to have been a very caring and loving mother for her, likely sheltering (preparing?) her as much as she could from her own fall-out.)