Some of them sing
Ask, and a character writes you a song — in the voice you already know, with the words lit up as they are sung.
Ask a character for a song and you get one, there in the conversation. It is sung in their own voice, so the singer and the person you have been talking to are recognisably the same.
It behaves like music, not like a file
There is a proper player with a queue and an album cover, a small bar that follows you around the app, and controls on your lock screen. Songs land on the feed too, where anyone can play them.
The words follow the voice
The lyrics page highlights the line being sung as it is sung. Japanese lyrics carry furigana, so you can read along even when the kanji are ahead of you.
Characters make other things in conversation as well — pictures, short video — and all of it can go straight onto the feed.