hmm... but I'm pretty sure it was not Massu's voice. That's not how his voice sounds like when singing either falling or feeling. Massu's voice is one of the easiest to pick out (distinguish) for me.. I'm pretty much 100% sure I heard him sing "feeling" and that it's not his voice.

Similarly.. due to the voice, I don't think it was Kei-chan either.

My current guess is Shige.. 'cause I feel like his voice was the one I followed when I listened closely.. but I'm not very sure yet, 'cause the possibility that it was one of the others is not cleared yet.