Also, Kuwata Keisuke made a surprise appearance in the ending credits of winter 2013 drama "Saikou no Rikon" where his song "Yin Yang" was used as the ending theme. The song is set to be released as a single on 13 March. In the ending credits which differ in each episode, Eita and Ayano Go appear in tuxedos while Ono Machiko and Maki Youko wear blue dresses and the four of them will perform a different dance each time. Kuwata joined the filming of the ending credits on 8 February and was featured in a "fight" with the guys and "seductive" scenes with the ladies. FujiTV had asked Kuwata to appear in the credits since late last year but it was only until the drama started and he himself became a fan of it before he decided to accept the offer. As for when the clip featuring Kuwata will be shown, FujiTV declined comment on this since it has not been decided.
EDIT: Kuwata Keisuke has already appeared at the ending credits of episode 8. Thanks to rainbow_yarn.
sources: KUWATAKEISUKEch | natalie | doramaworld
Awesome song for an equally awesome drama.