What is the name of the song played during the scene where Asuna is buffing the party underwater in SAO Extra Edition? The song I'm referring to is often called the "Underwater quest BGM", as it is first played when Asuna is buffing the party in the Extra Edition. The next time it is played is in SAO II episode 2 near the ending. 

Which album was the soundtrack placed in? Last time I checked, it wasn't in Volume 1 nor 2 of SAO II's OST.
That song's real name is 'Moon and shadow' and is the 19th song of disc 4 of 'Sword Art Online Music Collection' (ソードアート・オンライン ミュージックコレクション)
which was released on 2016.01.27 (Catalog Number SVWC-70116~9).