ORIGIN@L PIECES 04 is Kaoru, Hokuto, Kei, Kuro, and Saki. You can preview "Because" by Kaoru, " 流るゝ風の如く ~和敬清寂~" by Kuro, and "フェイバリットに踊らせて" by Saki in-game right now! The other tracks are "ROMANTIC SHAKER" by Hokuto and "Sanctuary World" by Kei.
This is definitely my favorite PIECES album so far! "Because" is giving me "Venus Syndrome" vibes and I'm gonna bet "ROMANTIC SHAKER" is a jazz song.