Meiko (Main lead singing)
Kaito (Male w/ blue hair)
Kagamine Len and Rin (The twins. Len is male, Rin is female)
Hatsune Miku (Girl with teal, long twintails)
Yowane Haku (Girl with grey hair)
Akira Neru (Girl with blonde sidetail)
Kasane Teto (Girl with reddish-pink hair)
Hachune Miku (Chibi/Deform version of Miku)
There are actually a lot more characters missing, but those are the ones I know of. Hatsune Miku and Kagamine Rin & Len are both part of the Vocaloid2 characters, while Meiko and Kaito were from Vocaloid. Kasane Teto is not actually from anything, rather her voice samples are from a software called UTAU. Hatchune Miku is a spin-off of Hatsune Miku herself. Yowane Haku and Akira Neru are both spin-offs of Miku also. As for Kamui Gakupo, I mentioned him because he was voiced by Gackt. To learn more about the spin-off characters themselves and/or find out more spin-off characters, the best place I’ve found so-far is here, so please take a look at their post and also there may be things I am missing.
As for the song itself. It originally was a Chinese (Mandarin) song by Cyndi Wang.