This is DLC you can play in Taiko Mode.

*Song: "Sayonara Elegy"
Easy: ★3 Normal: ★4 Hard: ★5 Extreme: ★8

*Song: "U.S.A."
Easy: ★2 Normal: ★3 Hard: ★5 Extreme: ★6

*Song: "Koi"
Easy: ★2 Normal: ★3 Hard: ★3 Extreme: ★6

More details on the official game page of Taiko no Tatsujin: Drum 'n' Fun! Pops Pack Vol. 1 ...