Koiiro Soramoyou Original Soundtrack

[Aye Sephra]

Some information about the BGM composers

http://www.exelion.jp/
Wow, EXELION composed part of the BGM of "Koiiro Soramoyou"

http://fairy-sound.sentive.biz/works.htm
Sei from SENTIVE also composed some of both "Koiiro Soramoyou" and "Koiiro Soramoyou after happiness and extra hearts"

Maybe there're more?

[Teioh]

Studio CUBE also lists involvement on their website
http://www.cube-sound.co.jp/zpr.html

Although exactly what they did is unknown (could be SE). Some of the games they list have other BGM composers confirmed (e.g. the Whirlpool games) or Nightshift Nurses 2

[Teioh]

A few years later, the staff roll should clarify some of the involvements.