Early career

Yamanaka made his professional debut against Kazuki Koyanagi on 22 June 2012. He won the fight by unanimous decision, with all three judges scoring the fight 40–36 in his favor.^[3] Yamanaka amassed a 6–1 record during the next two years, before being booked to face Hiroki Yamamoto in his first eight round bout on 6 April 2014. He won the fight by unanimous decision, with scores of 80–73, 80–73 and 80–74.^[4] This victory extended Yamanaka's winning streak to three fights, which earned him a fight against the #3 ranked OPBF minumumweight contender Roque Lauro on 22 August 2014. He lost the fight by split decision, with scores of 78–75, 75–77 and 76–77.^[5]

Yamanaka bounced back from his second professional loss with five consecutive wins, most notably beating Ronelle Ferreras by unanimous decision.^[6] This winning streak earned Yamanaka the right to face the former WBO mini flyweight champion Merlito Sabillo for the vacant OPBF mini flyweight title on 11 November 2016.^[7] He won the first twelve-round bout of his career and his first title fight by unanimous decision, with scores of 118–110, 117–111 and 119–109.^[8][9]

Yamanaka vacated the OPBF title on 1 February 2017, after just four months as champion. Masato Yamashita, chairman of Shinsei Gym where Yamanaka trained at that point, stated: "I want Yamanaka to fight for a world title next".^[10] On 18 March 2017, the WBO ranked Yamanaka as their #1 mini flyweight contender.^[11]

WBO mini flyweight champion

Return from retirement

On 9 December 2021, the Japanese Boxing Commission revised their rules to allow fighters who were diagnosed with intracranial hemorrhage to compete again, if they were cleared to do so by a physician. Ten days later, Yamanaka announced he would return to professional competition.^[22] He was booked to face Daisuke Sudo on 6 March 2022, in a light flyweight bout.^[23] Yamanaka won the fight by a fifth-round technical knockout.^[24]

Yamanaka moved up another weight-class in order to face the #15 ranked WBO flyweight contender Jonathan Taconing next. The bout was scheduled as the main event of the "REAL SPIRITS.81", which took place on 14 August 2022, at the Central Gym in Kobe, Japan.^[25] Although initially scheduled as a ten round bout, the fight duration was later changed to eight rounds. Yamanaka won the fight by unanimous decision.^[26]

Yamanaka faced the #3 ranked WBO Asia Pacific light flyweight contender Kosuke Ando for the vacant WBO AP title in the main event of "2nd WHO's NEXT", which took place on 6 May 2023 at the Korakuen Hall in Tokyo, Japan.^[27] He won the fight by unanimous decision, with scores of 120–107, 117–110 and 118–109.^[28] Yamanaka made his first title defense against Jayson Vayson on December 17, 2023.^[29] He lost the fight by a second-round technical knockout.^[30]