Hamuko telling Minato about her thoughts of suicide in chapter 92.
Minato telling Hamuko his thought of letting her die after he saved her in chapter 5.
Whenever Hamuko talks about her loneliness.
Whenever Hamuko get's or feels "betrayed", specifically by Minato. Her normal mood goes to complete and utter despair when her trust is broken and it's just saddening to see such a "cheerful" character act like that.
Hamuko telling yelling to Minato that after she and Shinjiro had sex, he didn't say "I love you" and Minato being unable to know how to reply to her, pretty disheartening since she convinced herself she loved him (Shinjiro), and the fact Minato told her he loved her after they had sex. It also makes you wonder, she seemed pretty shocked when Minato said that.
THE.LAST.FOURnote well, technically the last 3, they are the "endings"CHAPTERS! As a whole.If you aren't crying, you probably don't have a heart....