Spoiler

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The boy found out that he’s actually not an angel. He was a high school student and there was a classmate who always bullied him and on a school trip, the classmate accidently fell off and died in front of the boy alone. So everyone blamed him for that classmate’ death bc they were known to hate each other. Only his father tried to protect him. Our boy had to suffer a lot then killed himself and become the ‘angel’. Cb to present, he says that he now want to stay by Yukinori’s side. After that, they become closer and happier. But one snow day, when they’re playing together, he says that maybe his wish’s being loved wholeheartedly by someone. And now his wish is fullfied. After he disappeared, Yukinori suffers from depression and loneliness. When he finds a feather, he know it’s not just a dream then decides to live a better life and he thinks that it’s him whose wishes are fullfied. In a special edition, they finnally meet again in heaven.
I’m so sad TAT

And now i think i understand the oneshot published earlier. I thought that one’s ending was HE but it’s just OE. Cz seme’s wishes’s not fullfied yet so the angel can not comeback to heaven.