Oh man, I suck at explaining things... But well, I'll try.
Onyanko Club debuted in 1985 and was the biggest 80's idol group in Japan. It had 52 members in the end, some of them got very famous like Shizuka Kudo (Takuya Kimura's wife, I think) or Kokusho Sayuri (she was on a recent Pussuma episode with Yaguchi Mari). Onyanko Club also had their own TV show called Yuuyake Nyan Nyan.
Onyanko Club's first single was called Sailor Fuku wo nugasanaide and the lyrics were kinda... well, perverted? XD
Here's a link to the translation. They also had other "perverted" songs like Otto CHIKAN! and Oyoshi ni natte ne TEACHER. But they were very popular.
There were three sub-groups: Nyangilas, Ushiroyubi Sasaregumi (W's Nagisa no [...] is a cover of their song) and Ushirogami Hikaretai.
If you want to know more, I suggest you try Google.