In 2003, Mizushima entered All Japan Women's Pro-Wrestling (AJW) dojo, where she was trained by Animal Hamaguchi in not only professional wrestling, but also mixed martial arts.

[18] On December 31, Taiyo made her debut for NEO Japan Ladies Pro Wrestling, defeating Fuka for the Princess of Pro-Wrestling Championship, a title owned by the JDStar promotion.

[23][24] In April 2008, Taiyo and Nanae Takahashi left Pro Wrestling Sun and formed the Passion Red stable with Kana on the Japanese independent circuit.

[30] Passion Red made its debut for NEO on August 24, 2008, when Taiyo and Kana were defeated in a tag team match by Hiroyo Matsumoto and Kyoko Inoue.

[29] In their first six-woman tag team match on October 26, Taiyo, Kana and Takahashi defeated the trio of Etsuko Mita, Toshie Uematsu and Yoshiko Tamura.

[31] While feuding with the NEO originals led by Tamura, Passion Red also got involved with rival group Revolucion Amandla of Atsuko Emoto, Kyoko Kimura and Tomoka Nakagawa.

[32] On December 31 at Grand Final '08, Taiyo and Kana faced Ayumi Kurihara and Yoshiko Tamura in a match to determine the number one contenders to the NEO Tag Team Championship.

[33][34] The Passion Red duo received their shot at the NEO Tag Team Championship on February 21, 2009, but were defeated by the defending champions, Atsuko Emoto and Kyoko Kimura.

[26][39] On July 25, Taiyo made her first High Speed Championship defense, defeating Io Shirai, and followed that up by successfully defending the title against Fuka on August 29.

[9] The following month, Taiyo formed the tag team Kawasaki Katsushika Saikyou Densetsu with the recently debuted Yoshiko, the two defeating Iris and Yoko Bito in their first match together.

[53] In February 2012, the recently debuted Act Yasukawa joined Taiyo and Yoshiko as the third member of Trouble Maker 2, effectively replacing Yuu Yamagata, whose Stardom appearances became more irregular.

[54] On May 3, Kyoko Kimura turned on Miho Wakizawa and joined Taiyo, Yoshiko and Yasukawa as the fourth member of their newly renamed stable, Kawasaki Katsushika Saikyou Densetsu Plus One, often shortened to Kawakatsu-gun.

[58] On June 24, Taiyo led Kashima, Yasukawa and Yoshiko to a win over Kairi Hojo, Yoko Bito, Yuhi and Yuzuki Aikawa of Zenryoku Joshi in an eight-woman battle of the stables.

[61][62] On October 27, Taiyo and Yoshiko entered the 2012 Goddesses of Stardom Tag League, suffering an upset loss against the team of Io Shirai and Mayu Iwatani in their opening round-robin match.

[61][66] On December 31, Taiyo and Nanae Takahashi reformed Passion Red for a special appearance at Ice Ribbon's RibbonMania 2012 event, where they defeated Muscle Venus (Hikaru Shida and Tsukasa Fujimoto) in a tag team match.

[70][71][72] Six days later, Taiyo and Yoshiko defeated Thunder Rock (Io Shirai and Mayu Iwatani) to make their second successful defense of the Goddesses of Stardom Championship.

[70][73] On March 3, Taiyo made her third successful defense of the High Speed Championship, when she wrestled freelancer Kaori Yoneyama to a thirty-minute time limit draw.

[85][87] On August 17, Taiyo also attempted to regain the Artist of Stardom Championship with stablemates Act Yasukawa and Yoshiko, but the three were defeated by the defending champions, Kairi Hojo, Kaori Yoneyama and Yuhi.

[8][93] On January 12, 2014, Taiyo celebrated her tenth anniversary in professional wrestling by reuniting with Nanae Takahashi in a tag team main event, where they defeated Mayu Iwatani and Yoshiko.

[12][105][106] Following Nanae Takahashi's departure from Stardom, she held a press conference on June 12, 2015, to announce "Seadlinnng", a new professional wrestling production company with Mizushima serving as its senior managing director.

[2] Mizushima, billed as "Natsuki Taiyo" (without the star in her ring name), also began working for Seadlinnng as a referee,[7] making her debut in the role at the promotion's first event on August 26.

[6] In 2011, Mizushima had a minor acting role in the Welcome to the El-Palacio television drama, where she appeared alongside fellow Stardom wrestlers Nanae Takahashi, Yoshiko and Yuzuki Aikawa.