[2][3] He was promoted to the rank of apprentice professional 3-dan in April 2017 and obtained full professional status and the rank of 4-dan after finishing third in the 67th 3-dan League (April 2020 – September 2020) with a record of 13 wins and 5 losses.
[2][3][4][5] Although Koga's third place finish was not sufficient to earn him direct promotion to 4-dan, it was good enough to earn him a second promotion point which gave him the option to enter the professional ranks as a free class player.
After consulting with his mentor Nakata, Koga decided he wanted to turn professional even if it meant starting in the Free Class.
[2][3][a] In September 2021, Koga was promoted to Meijin Class C2 after defeating Hirotaka Kajiura 7-dan to reach the finals of the 52nd Shinjin-Ō [ja] tournament.
Koga's victory meant that he satisfied the criteria for promotion to Class C2 for the 80th Meijin League (April 2022 – March 2023).