[1] At the age of 21, Yamamoto made a transition from wrestling to mixed martial arts despite his father's opinion that MMA is not a real sport.
[2] Yamamoto made his professional mixed martial arts debut on March 2, 2001, against Masato Shiozawa at Shooto - To The Top 2, where he won by unanimous decision.
During this time Yamamoto faced future Strikeforce Lightweight Champion Josh Thomson in Honolulu, Hawaii, at Shogun 1.
Yamamoto dominated Thomson with takedowns and strikes but caught an accidental kick to the groin three minutes into round two, causing the bout to be ruled a no contest.
Over the next year, Yamamoto's popularity grew as he went on to defeat Kazuya Yasuhiro, Jadamba Narantungalag and Ian James Schaffa in exciting fashion.
Yamamoto would then write his name into K-1 Hero's history by defeating three highly regarded fighters—Royler Gracie, Caol Uno and Genki Sudo—to win the 2005 Middleweight Grand Prix.
[3] On May 3, 2006, Yamamoto made mixed martial arts history when he knocked out Kazuyuki Miyata four seconds into the fight with a flying knee moments after the bell sounded.
[4] In early 2007, Yamamoto announced an indefinite leave of absence from MMA to go back to his roots and train for and compete in freestyle wrestling for the 2008 Summer Olympics in Beijing.
With this injury, Yamamoto had no choice but to leave his hopes of competing in the Olympic Games and return to mixed martial arts.
[10] In preparation for the fight Yamamoto decided to "reinvent" himself, moving to Okinawa to train under former WBA Light Welterweight Champion Akinobu Hiranaka.
[18] Yamamoto rocked Lee early in the opening round with a right hand, but minutes later was wobbled by a right hook-uppercut combination from the Brit.
[21] The bout was declared a no contest after an accidental eye poke by Yamamoto rendered Salazar unable to continue midway through the second round.
[28] Kid Yamamoto lost to Amateur Kickboxer Percy Ramos, at the Fighter of the Year tournament, 2006 by TKO into the fourth round.
Yamamoto then faced Mike Zambidis at the K-1 World Max 2005 Tournament, he would also lose this bout by KO early into the third round.
Yamamoto was married to Japanese female fashion model MALIA (マリア,新保真里有), with whom he had two sons and a daughter.
In the beginning of 2018, Yamamoto's condition worsened to a point where his father flew him to Guam to receive treatment for his terminal cancer.