A Kylie Minogue cover.
According to the Youtube comments this was their last TV performance, that’s why one of them is upset.
2019 edit: Again, the video’s been taken down, so I’ve had to replace it with one I just kinda liked.
2020 edit: And gone again, so I’ve found what I think is the original one and uploaded it. I’ve also learnt the tears are because they were moved by their song becoming number one in Japan.