As far as i know Fishmans+ was a sort of tribute project formed to mix and release this "lost" track (apparently only played live shortly before the breakup of the band) and for a subsequent tour featuring the surviving Fishmans members featuring a cast of guest musicians. The art of the single was made by Yamantaka Eye of Boredoms, and I think the final mixing was done by Ryuichi Sakamoto, but i'm not sure.
Hello