Why did Ayu cry in one of her 'Heaven' live performance

[fossil]

I was watching her Heaven' live performance video, she had this white T-shirt on, and red wrist band (you know for basketball) on right hand, and black one on the left hand, and half way through the song she started tearing up.

I know the song is kind emotional, my question is did she do that for a special occassion? or just felt sad for obvious reasons unknown to me