Aya Hirano, Chihara Minori, and Yuko Goto, the seiyuu of Haruhi, Yuki, and Mikuru (respectively) from the anime Suzumiya Haruhi no Yuutsu (The Melancholy of Haruhi Suzumiya) performing Hare Hare Yukai. For the encore Tomokazu Sugita (Kyon) and Daisuke Ono (Koizumi) join in. It's the same concert ( Suzumiya Haruhi no Gekisou )in Lucky Star  ep 15 Hai hai! mite mite! see in the other Video. ^^