Where does "a song is born" belong to?

[channy]

I am organizing my Ayu singles and I wonder where I should put "a song is born" with Keiko? Is this single part of Ayu's discography? Or is it like "Happening Here" which was released under Ayu's name but not as part of her discography?

I have "poker face" to "L" in a folder called "Regular singles", then the reissued singles "poker face" to "TO BE" in "Re-released singles" and "Together When..." and "how beautiful you are" in "Digital singles".

Now tell me, what should I do with "a song is born"? xD

Edit: Maybe I should create a folder called "Charity singles" for "a song is born"? o.ô