[Aoi Kurenai]

And completely out of left-field, it looks like the song was originally going to feature TM Revolution instead of ISSA.

It's such a shame, the voices more distinct here so it's easier to tell them apart.

My only guess as to why they did this is because ISSA's experiencing a massive resurgence in popularity. His group, DA PUMP, was thought to be way past their prime but had a huge hit over the summer. ("U.S.A.", it was one of those "so lame it's cool" deals, inspired memes and challenges online) I'm guessing maybe Avex wanted him while he was in the limelight again.

ISSA is signed to Avex Trax, the label Rider uses for music, TM Revolution isn't. I'm guessing this was going to be a "it's an anniversary so we'll cross party lines to get someone really big" deal but when ISSA turned out to be really popular again, this seemed like the easier route.