Early years
Koja was born on 23 October 1983 in Naha, Okinawa.
After graduating from the Faculty of Pharmaceutical Sciences at the University of Tokyo, Koja entered the Graduate School of Pharmaceutical Sciences at the same university but dropped out. In 2008, he joined the Ministry of Internal Affairs and Communications (MIC) and was seconded to places such as the Nagasaki Prefectural Government.
He resigned from the Ministry of Internal Affairs and Communications in 2020. Following his resignation, he joined NTT Data Institute of Management Consulting, Inc., where he was involved in human-centered urban development leveraging information and communications technology, as well as training programs for startup founders in Okinawa.
Political career
In the lead-up to selecting a candidate for the Okinawa at-large district in the 2022 House of Councillors election, Kosaburo Nishime, a Liberal Democratic Party (LDP) member of the House of Representatives, approached Koja about running as an LDP candidate. Accepting the request, Koja decided to run and announced his candidacy. In the election, he narrowly lost to the opposition-backed incumbent Yōichi Iha by a slim margin of 2,888 votes.
On 21 December 2022, he took office as Deputy Mayor of Naha City under Mayor Satoru Chinen.
Governor of Okinawa Prefecture
On 11 January 2026, ahead of the gubernatorial election scheduled for that year, economic and conservative organizations in Okinawa Prefecture nominated Koja as their candidate. On 6 February, Koja stepped down as Deputy Mayor of Naha City, and on 23 March he officially announced his candidacy.
On 27 August, the gubernatorial election campaign officially commenced. Shortly before the announcement, conservative candidate Mikio Shimoji withdrew his candidacy, turning the race into a virtual head-to-head battle between Koja and incumbent left-wing candidate Denny Tamaki. Koja's political platform aligned with conservative, pro-Taiwan stances and supported Japan's defense policies alongside Western nations and the United States.
On 13 September, as a result of the election, he defeated Tamaki by a large margin and became the next governor of Okinawa Prefecture. He became the first Governor of Okinawa Prefecture born after the 1972 reversion of Okinawa to Japan.
