The streams feature looped recordings performed by Furyuya and Mitsuishi, and they will broadcast for 24 hours beginning at 12:00 AM JST on Constitution Memorial Day (May 03, 2018).
The streams can be found here for Tōru Furuya and here for Kotono Mitsuishi.
Niconico will also be streaming the documentary “Constitution of Japan: The Movie”, which features interviews with intellectuals from all around the world about the 1947 establishment of the Japanese Constitution, beginning at 9:00PM JST, but unfortunately for the history buffs in the audience, this stream is region-restricted to Japan only.