She is singing the ending theme to Saki.

I love that song, but I hate myself for that. And tacos. I crave tacos now. Dammit.

Not the whole, song, I mean. Just the part where they wave their stubs in the air and go "Wai, wai". And the part where Yuuki eats the tile.

SATSUGAIIIIIIIIIIIIIIIIIIII!!!!!!!!