This CD contains a character image song for the TV anime Nogizaka Haruka no Himitsu (乃木坂春香の秘密).
The tracks are as follows.
Track 2 "Hitosashiyubi Quiet!" is a solo version by Mamiko, but it also contains some chorus parts by the other girls.
Track 4 is a short talk by Mamiko as Haruka (around 1 minute).
[Nogizaka Haruka no Himitsu CDs]