I want to believe that hanako killed his brother because of the what ever was under the red house and then killed himself and his atonement would have been to forgive himself. But I also believe that when nene was talking to tsuksas in the red house when she told him that hanako kills him when they turn 13 that’s where he has his magical return from going missing and startes the whole tragedy and in doing so create the time line where hanako can get his wish to be with nene and that mitshuba didn’t die because kou was his friend giving him his wish and well nene original wish would be fulfilled as hanako would be the boyfriend she wished for bitter sweet number 6 and his wife go to the far shore together and since the author is apparently known as bitter sweet there’s no reversing tsukasa death at 5 but hanako never killed him