[Corvina]

I guess, I don't really understand what you mean.
She talked about it in one of the many interviews she did though, recording it new.
And maybe it also helps you understand the album better, going throug one of the interviews, Idk.

But with tie-in songs it sometimes isn't easy to include them in own releases. No Kame Rider song was ever released outside of Kame Rider related releases. Kuu's is the first. Maybe because her husband wrote the song and they haven't given away all of the rights for it.