Because she got to play her 'ballad' at the show, concerto they used to distract Angel... in AB, if you disappear, it's because the person achieved what they wished... for Iwasawa, it was playing that song, which achieved a certain state of mind she wanted and so she disappeared.
Basically what they said. Her dream was to play her songs for others and help them. So when she sang her song and realized that she'd finally achieved her goal/dream, she accepted her fate and disappeared.
If your pergunta is why did she disappear or how do people disappear I can answer both first of all I’ll do how I think people disappear when they do something that they can’t do in they’re actual life Like Iwasawa she sang a song that she couldn’t do in her life Somewhat like Hinata he almost maybe disappeared if caught that ball welp there’s your answer
