Both women feel worthless, yet Konno ironically keeps trying to give Yumimaru hope and confidence. Renting a friend and her object of adoration is incredibly sad and desperate, but I think Konno is also motivated by compassion. Even two chapters in, I relate to the characters. The artist previously created an amazing manga involving a different countdown and the writing is great, so my hopes are sky high. Still less dark than that other summer manga..
I don't get what's bad about having your farewell letter read at your funeral... But then I have trouble with that kind of things in general. I have no idea what hurts others when it comes to death or love. (and since I'm depressive and suicidal myself I always end up hurting people by mistake :( )
I'm honestly conflicted about answering, but taboo is counterproductive, and that's a valid question:
At minimum, words from beyond the grave will force the mourners to grapple with a present-tense persona they've already been thinking of in past-tense, and who they will never meet again. I wouldn't call it "vengeful" but it is knowingly inflicting a kind of disorienting pain even if the words are comforting. For someone distant from family, or passive-aggressive in the slightest, a note would be a reminder of that distance and lack of reliance. For a suicide, the farewell letter is surprising most or all of the mourners with a suicide note, which further emphasizes how each of them was in the end useless to the deceased. I'm not saying a farewell letter can't be done well, and I think even family has no right to be possessive about someone's life nor how they handle death. "Ruining" one's own funeral is rad. A snarky or vengeful farewell letter is an interesting way to burn out, especially as a footnote to fighting, raging, to survive.