>>280077353Here is the relevant study, the sample size was over 800 people.
https://journals.sagepub.com/doi/10.1177/0956797611417007
Here's the follow-up study if you want to pay for access.
https://www.jbe-platform.com/content/journals/10.1075/ssol.3.1.09lea
This is just another case of people not knowing what they want. And besides, if I were to attempt to avoid spoilers, there would be no way to convey what an altogether unpleasant experience the manga is. How do you warn someone that characters are going to die without saying that characters are going to die? "Dude be careful, it's a tragedy"? That means the exact same thing.