"proof of life" is the answer song to Hitoshizuku-P's hit song "soundless voice", first uploaded on November 28 on piapro. "soundless voice" was quite popular, with over half a million views, and a month after it was uploaded, Hitoshizuku-P uploaded an "answer song" to tell Rin's version to the story. The story of Rin, who was apparently dying. She tried to convince herself that everything would be alright and kept on singing. Even with Len comforting her she still couldn't deny the fact that her time would be up. In the end she died, with her last words being "thank you".