[Kakeru]

Well the thing is that until recent years, Do As Infinity has always listed "D.A.I" as their own lyricist & musician. Many assumed it was just Dai Nagao, when in fact some songs (eg. "AZAYAKANA HANA" on "GATES OF HEAVEN") was written solely by Ryo Owatari & some lyrics were written by someone other than the 3 members (for that reason, Do As Infinity has ALWAYS claimed "Do As Infinity is composed of the 3 members AND ALL SUPPORTERS). So that could also be the case for Ayu's songs. Although I think it's safe to say that Dai Nagao himself did most (if not all) of the compositions for other artists, & in this case, ya, Ryo probably helped out.