I understand why people are mad about Ash's ending. I understand why we're are all sad, but really think about. Ignore what the writer has said and think about the storyline.
The ending was sad, but it was a harsh reality. A reality that has given him peace. I just feel sick to my stomach. Ash knew he couldn’t just turn his life around like nothing ever happened and move away with Eiji. He realized that he could never escape the world he’s in and the past that haunts him. What really hurt the most was knowing that Ash has always taken such hard hits, but always got back up and fought. He wanted to fight and punish the ones that have made his life and others a living hell. He went back into the library because he knew he and Eiji would always live in different worlds. Even though he was used to taking those hits and getting back up, he didn’t this time. The reason being is he didn’t have anything to fight for anymore. He got his revenge and those who needed to be punished were gone. He avenged the deaths of those he cared for. He also knew Eiji was safe and would always care for him no matter what. That letter and all these factors made him feel calm. His body is used to taking these hits and relying on the adrenaline rush to push him to continue, but that state of calm he felt because everything was over, pushed him to the edge. His frail eighteen year old body finally had to stand on its own and it lost.
Ash was just a child. Ash has suffered anorexia, low blood pressure, insomnia, depression, trauma we will not mention, multiple life threatening wounds, a broken family, and witnessed loved ones die because of him. Truthfully he shouldn't have even been alive from episode 1, but I am proud of the character development he had. Its a hard pill to swallow, but Ash would have ended it himself eventually if Lao hadn't done anything. Even after meeting Eiji, Ash never strayed from the idea of ending things himself. Eiji was a breath of fresh air and I'm glad those little moments of them spending time together was included. It gave him a sliver of that normal childhood he's missed out on. Ash didn't 'deserve' to die as the writer had pointed out, but Ash needed it in order to set him free. Not because of what he has done, but because of how much he suffered.
If there was an OVA made, I wouldn't want it to be where Ash just goes to Japan after reading the letter. I would want to change it from the beginning. A parallel universe where Ash doesn't meet Dino after his childhood trauma. Maybe one where Ash transfers to Japan and meets Eiji in school. Imagine how heart warming it would be to see Ash have a good teenage life. Like what if Ash was still intelligent and got to go to college early and meet Eiji there after Eiji's accident. They would become each other's saviors without their life being threatened every damn second. *grabs heart and sobs*