The biggest theme in this story, is human relations and how they can force you to do something that you didn't even want to do.
It starts with a regular middle school that had a bullying incident, where 4 people were bullied by one person, and one ending up committing suicide. But the mystery is that the actual bullying stopped months ago, and the suicide had come out of nowhere. The suicide victim left a will saying that Taku Sugawara is the devil and nobody should believe his words, but he has been monitored for months and there is no proof that he has interacted with the suicide victim at all. Trying to find out the truth, the sister of the suicide victim goes out to try and find out why. At the end it turns out the one who commited suicide (Masaya) and 3 others were the ones bullying Taku Sugawara.
I didn't like the end but well.... even Taku said the ending was "warm".
"Trash won’t be able to get a happy ending"
"Because this ending is so warm"
"Ahh, maybe I’m no longer trash"