Also when Isamu is about to just let himself plummet to his death... and what saves him? Hearing Myung sing Voices in a small, soft, helpless voice.
In the movie version: Sharon's death. More exactly, when her destroyed AI is short-circuiting in what's equivalent to her last breath, sorrowfully asking what did she do wrong since she loved Isamu and simply wanted to fulfill his wish. And then there's Myung holding Sharon's AI carcass and whispering to her, first sadly explaining what did go wrong...and following it with just as sadly explaining that she had been doing the same herself.