A native of Otsu, Shiga Prefecture, Mikazuki joined the West Japan Railway Company in 1994 after graduating from Hitotsubashi University's Faculty of Economics.

Mikazuki entered the House of Representatives as a member of the Democratic Party of Japan after winning the Shiga No.3 District in the 2003 general election.

At the 2005 general election he survived the "hurricane" victory by Junichiro Koizumi's ruling Liberal Democratic Party, retaining his seat by a margin of 266 votes (0.17%) over LDP candidate Osamu Uno.

He lost his position in the cabinet in a September 2010 shuffle and was instead appointed deputy chairman of the party's national policy committee.

Aichi: Hideaki Ōmura Akita: Norihisa Satake Aomori: Sōichirō Miyashita Chiba: Toshihito Kumagai Ehime: Tokihiro Nakamura Fukui: Tatsuji Sugimoto Fukuoka: Seitaro Hattori Fukushima: Masao Uchibori Gifu: Hajime Furuta Gunma: Ichita Yamamoto Hiroshima: Hidehiko Yuzaki Hokkaidō: Naomichi Suzuki Hyōgo: Motohiko Saitō Ibaraki: Kazuhiko Ōigawa Ishikawa: Hiroshi Hase Iwate: Takuya Tasso Kagawa: Toyohito Ikeda Kagoshima: Kōichi Shiota Kanagawa: Yūji Kuroiwa Kōchi: Seiji Hamada Kumamoto: Takashi Kimura Kyoto: Takatoshi Nishiwaki Mie: Katsuyuki Ichimi Miyagi: Yoshihiro Murai Miyazaki: Shunji Kōno Nagano: Shuichi Abe Nagasaki: Kengo Oishi Nara: Makoto Yamashita Niigata: Hideyo Hanazumi Ōita: Kiichiro Satō Okayama: Ryuta Ibaragi Okinawa: Denny Tamaki Osaka: Hirofumi Yoshimura Saga: Yoshinori Yamaguchi Saitama: Motohiro Ōno Shiga: Taizō Mikazuki Shimane: Tatsuya Maruyama Shizuoka: Yasutomo Suzuki Tochigi: Tomikazu Fukuda Tokushima: Masazumi Gotoda Tokyo: Yuriko Koike Tottori: Shinji Hirai Toyama: Hachiro Nitta Wakayama: Shūhei Kishimoto Yamagata: Mieko Yoshimura Yamaguchi: Tsugumasa Muraoka Yamanashi: Kotaro Nagasaki