It's not just the deaths. It's more of Rintaro's psychological state. Imagine, having to undo everyone's happiness that "he granted" with his discovery. It was beyond heart breaking for me to watch. One by one, he granted everyone's desires. It was all uphill for him, and then after that, he has to tear it all down, and only he would remember every bit of it.
That's when I thought, "To save the thing most precious to you, to make things right, how much of others' happiness do you have to destroy?"
Things must be set right, things have to go the way they have to, but is it for the best for you or for everyone?
I hate thinking, and I hate anime that makes me think about things analytically. But this anime hits a psychological nerve, and if everyone thought about it, you'd realize that it's something the average person thinks about: "If there was something I want to change in the past, what would it be?" And it's always a thought about you, and not about the repercussions it could cause.