If I remember correctly, Kobayashi does the porn under a different name, doesn't she?
I think, it used to be Hiromi Morita but now it is Karin Hayashi.
Here is a few facts and timeline that I (shamelessly) translated from:http://ja.wikipedia.org/wiki/%E3%82%AB%E3%83%B3%E3%83%88%E3%83%AA%E3%83%BC%E5%A8%98%E3%80%82
April 1999 - Audition sucess for Rinne Toda, Hiromi Yanagaihara, and Azusa Kobayashi's 3 person formation of Country Musume.
July 1999 - A incident just before the release of "Futari no Hokkaido", Hiromi Yanagaihara sudden death by a traffic death.
August - Azusa Kobayashi worrying leads to a withdrawal
May 2000 - Asami agrees to join. Rinne Toda changes name to Rinne.
July 2000 - First Starring Movie "Kantorii Gaaru Hokkaido Bokujou Monogatari" presenting to the public, theme song "Koi ga Suteki na Kisetsu" release.
April 2001 - Rika Ishikawa (At that time a Morning Musume. member, currently graduated) is a guest with "Hajimete no Happy Birthday!" as major debut.
January 2002 - Mai Satoda joins
October 2002 - Rinne, wanting to study stage, graduates
May 2003 - Miuna joins. July's "Uwaki na Honey Pie", guests Miki Fujimoto and Asami Konno substitutes.
August 2003 - Mai Satoda becomes a member of ROMANS
November 2003 - Major Debut after clip assembles "Country Musume. Singles V Collection 1" sale.
Azusa Kobayashi of Country Musume. previously took the stage name of Hiromi Morita (http://www.book-style.com/GARO/gapg0601.jpg
(?)). Nowadays her public stage name is Karin Hayashi (http://d.hatena.ne.jp/images/ean/4511749010091.jpg
) for public public entertainment and doing resumption.
Hiromi Yanagihara of Country Musume previously starred in a drama "Taiyou to Umi" (1998) with Morning Musume. and movie "Morning Teishi ~Daite HOLDONME!~" [aka Morning Cop] (1998).
Idol wo Sagase! (2000, TV Tokyo, Rinne is with Kaori Iida to work for chairmanship)
Oosaka Denki DASH! DOYAH (2001-2005, BS2)