[1][9] While living in Los Angeles, California, she studied some of her elementary school years before returning to Japan following her mother's unexpected death.
[10] Yamaguchi began to learn karate during her residence in the United States around the age of 7, yearning to be like Jackie Chan.
[14][15] On September 6, 2007 (2007-09-06) at Smackgirl 2007: Queens' Hottest Summer, Yamaguchi defeated Emi Tomimatsu by split decision, winning the final of the Next Cinderella Tournament 2007 in the lightweight division.
[34] Yamaguchi became Valkyrie's Featherweight Champion in what is considered one of the biggest upsets in the history of women's mixed martial arts.
Yamaguchi barely retained with a contentious majority draw in which the dissenting judge scored the fight in favor of Takabayashi at Valkyrie 08.
[52][53] Yamaguchi fought outside Japan for the first time in her MMA career when she faced Katja Kankaanpää at Botnia Punishment 11 on March 23, 2012 (2012-03-23) in Finland.
[65][66] In her second fight outside Japan, Yamaguchi faced Patricia Vidonic at Pacific Xtreme Combat 40 on October 25, 2013 (2013-10-25) in Guam.
[72] In her sophomore bout in the promotion, Yamaguchi faced Ayaka Hamasaki at Deep - Dream Impact 2014: Omisoka Special on December 31, 2014.
[75] In May 2015, Yamaguchi entered into a single-day, four-woman featherweight grand prix which would crown the vacant Jewels Atomweight champion.
[81] In her sophomore bout in the promotion, Yamaguchi faced Istela Nunes at ONE Championship: Heroes of the World on August 13, 2016.
[89] Despite knocking Lee down multiple times during the bout, Yamaguchi failed to capture the belt in her second attempt, losing via unanimous decision.
[90] After the title shot loss, Yamaguchi faced Jomary Torres at ONE Championship: Destiny of Champions on December 7, 2018.
[100] The bout with Bo Meng was rebooked for the third time to take place at ONE Championship: King of the Jungle on February 28, 2020.
[103] Yamaguchi faced Julie Mezabarba as part of an alternate bout for the Atomweight World Grand-Prix at ONE Championship: Empower on September 3, 2021.
[105] Yamaguchi faced Jihin Radzuan at ONE: Bad Blood on February 11, 2022, as a late notice replacement for Jenelyn Olsim.
[107] In order to finish her career in her native Japan, she was granted an early release from ONE and subsequently signed with Rizin Fighting Federation.
[108] She dropped to super atomweight division and made her promotional debut against Kanna Asakura on April 29, 2023, at Rizin Landmark 5.
[111] Yamaguchi tried her hand in submission grappling, first in the Abu Dhabi Combat Club Japan Trial final qualifier in the under-55 kg class, where she was defeated by points by Yasuko Mogi on April 15, 2007 (2007-04-15).
[112] In her second and final submission grappling match, she was once again defeated by points; this time by women's MMA star Miku Matsumoto at DEEP X03 on July 5, 2008 (2008-07-05).
She began competing on August 23, 2009 (2009-08-23), in the shoot boxing tournament Girls S-Cup 2009, where she defeated by decision South Korean female Muay thai kickboxer Su Jeong Lim and fellow mixed martial artist and karateka Madoka Okada before losing against female shoot boxing rising star Rena Kubota in the tournament final.
She participated in the shoot boxing Girls S-Cup 2010, defeating Samanta van Dole by technical submission (standing guillotine choke) and losing against Ai Takahashi by unanimous decision after an extra round.
[122][123] Yamaguchi was scheduled to compete against Du Peiling at the 2013 Shoot Boxing Girls S-Cup Japan Midsummer Festival on August 3, 2013 (2013-08-03).