Talk:HuPC49/@comment-3570595-20190127203750/@comment-37117761-20190127212748

We cut to Emiru meeting New Ruru for the first time, then to another scene, then back to Emiru and New Ruru doing their song together. It's not unreasonable that between these scenes, Emiru taught New Ruru the song.

Then again, it's also not unreasonable that Dr. Traum copied Ruru's memories before she returned to the future and entrusted the copy to Emiru to use to create a new Ruru.