The Shinsengumi is not just a creation of the RK world, they actually existed, serving as the protectors of Kyoto before the Meiji Resotration. They were called Miburo -meaning Wolves of Mibu- because that is where they were stationed. Because at the time suspicious people usually ment trouble, many newcommers were cut down by the swords of the Shinsengumi. They weren't always popular though. During June of 1864 the Ikeda-ya Affair launched them to the status of heros when they killed Ishin Shishi members who were plotting to overthrow the Shogunate government.

The Shinsengumi consisted mostly of ronin samurai, and was originally led by Serizawa Kamo. However, internal conflicts caused both his and his vice commander, Niimi Nishiki's assassination. At the end of the Tokugawa Era, these were their officers.

Commander: Kondo Isami -.- Vice Commander: Hijikata Toshizo
Military Advisor: Ito Kashitaro -.- Spys: Yamazaki Susumu and Shimada Kai
-.- Squad Captains -.-
First: Okita Soushi -.- Second: Nagakura Shinpachi
Third: Saitou Hajime -.- Fourth: Matsubara Tadaji
Fifth: Takeda Kanryuusai -.- Sixth: Inoue Genzaburo
Seventh: Tani Sanjyuuro -.- Eighth: Toudo Heisuke
Ninth: Suzuki Mikisaburo -.- Tenth: Harada Sanosuke

Media in which the Shinsengumi show up:
Rurouni Kenshin (Kyoto Arc, OVA)
Rorouni Kenshin Manga - Watsuki Nobuhiro - Jump Comics
Peacemaker - (some name I can't read) - Gangan Comics
Soshite Haru no Tsuki - Ikushima Miya - Hanaoto Comics (!!!yaoi!!!)
Burai - Iwasaki Youko - Asuka Comics / Kadokawa
Bakumatsu Seishun no Hanafubuki - Kamo Nabako - Biblos (!!!yaoi!!!)
Kaze Hikaru - Watanabe Taeko - Flower Comics
Gohatto (film)
Shinsengumi Internet Radio - http://www.sir.mausu.net/ - (What is this?!?)