Why... feat URATA NAOYA
 

I've downloaded the Five album in here, and there's one track I didn't even knew existed; Why... feat URATA NAOYA.
Can anybody tell me where this is from?
It seems that there is a hidden track on BRILLIANTE in the iTunes download version (... which I've seen in another download thread in here) - is it that, or?

I think is the hidden track on BRILLANTE, in the CD+DVD version

Really? Thank you :)

yeah it's a hidden track found only in the CD + DVD pressing of FIVE & it starts after BRILLANTE finished

I wonder who did the arrangement for this version.. Yuta Nakano again? it isn't revealed since it's the secret track right?