Hatsune Kaidan (初音階段) is an experimental project by JOJO Hiroshige (JOJO広重) and Toshiji Mikawa (美川俊治) from Hijokaidan (非常階段) and Kamin Shirahata (白波多カミン), with Hatsune Miku (初音ミク) in background. Kamin and Miku are singing the same line at the same time.
The event was called 黒光湯の大政奉還 2013.