The hook is great: People start receiving suspicious mails that just list a body part. Soon after, that body part disappears from them bloodlessly and with no pain. It's a great setup for a horror mystery... Unfortunately, it's not what this series is actually about and sits firmly in the background.
What the series is really about is the relationships between people, what keeps society running. How we combat hatred with love and hope, despite all experiencing selfish desires. It's an uplifting message, but it's not really what the series promises at the start and the execution is so-so. Characters disappear from the story rapidly, for instance, the first victim who is both the female lead's sister and male lead's girlfriend, someone who feels like they should be relevant to the story, simply doesn't show up any more after the initial incident. It's effectively a story with only three characters, and everyone else only exists to service the plot before being shuffled away. How can you write a story about collective love and not have characters interacting with each other? It's bizarre.
The MC also feels pointless in most scenes. Pretty much the entirety of the manga is actually about the male lead and the antagonist. Her only real moment is the breakthrough at the very end, which could just as well be serviced by the male lead. Is it because this is shoujo, they feared making a guy the main character? It's odd.
The mystery itself is handled bizarrely as well. No one ever reacts to people losing their body parts after the initial shock. They are removed from the narrative and there is no large movement about not using phones or the treatment of these people despite it happening en masse at one point.
The ending is also just... Odd. The antagonist has a change of heart, but then decides to make a major immediate choice that doesn't align with that change of heart. There's the possibility they did so out of regret for their actions, but the work doesn't actually address that in anyway, he just does the thing and the series ends. It feels like the author wanted a melancholic end but didn't quite know how to actually get there.
As for the antagonist... his motivations are iffy. Some things just flat out don't make sense. The narrative expresses him as unable to experience or understand certain things due to physical limitation, but he experiences and reacts to those same things earlier in the series. He's also obsessed with humans being cruel and selfish, but no one who talks to him ever asks him why then he enacts his own cruel and selfish desires on others, calling him out on the blatant hypocrisy. It feels like a big gap in the motivation the author kinda just didn't have an answer for and ignored.
Perhaps this series would be better understood or enjoyed if I had also read "Motto, Ikitai... Install" which is another work by the same author I assume is a sequel or spinoff, but it has not been translated and I can't find raws for it either, so I doubt that will be happening anytime soon.