It was initially, but a couple days before it was changed to a single A-side, I think Sayu and Tsunku wrote about that
Man, up until seeing it on this list I've always thought Sayu was just kidding because it got no promotion aside from the MV.
So, the only single in the 10+ years that Sayu's been in MM, that Sayu was the lead singer (not a lead but THE lead) isn't even an A-side? It not just that. It was SUPPOSED to be an A-side, but they took that away from her............