On August 4th, 2018, Koyamada was elected as At-Large National Board of Directors of Sister Cities International (SCI) with top vote numbers among other 16 candidates of mayor, elected officials and business leaders at its annual conference and election held in Aurora, Colorado. The year of 2018 would be his second year to serve as the board member and first time to be elected as its At-Large Board member for three-year terms.
Sister Cities International’s Board of Directors is elected by its voting members—local cities and sister city organizations. The board elections include both electronic voting as well as in-person voting at the Annual Business Meeting held during Sister Cities International’s Annual Conference each year.
In 2017, Koyamada was first appointed by its Chairman as the Young Professional national board member for a year. In its first year of serving as the board member, Koyamada was awarded Chairman's Choice Award at 2018 Annual Conference in Aurora, Colorado for giving substantial contributions and achieving accomplishments he gave to SCI, including the following;
- Two separate international trips to Japan with two major sister cities delegations such as San Jose, CA and San Francisco, CA;
- Eight U.S. domestic sister cities trips for different occasions such as Virginia Beach, VA for its first annual conference; Annapolis, MD, San Antonio, TX and Aurora, CO for the quarterly board meetings; San Diego, CA for Thelma Press receiving Japanese government's Order of Rising Sun Award; Bakersfield, CA for California Sister Cities Joint Board Meetings; San Jose, CA for meeting with San Jose City Councils and San Jose-Okayama Sister Cities boards and leaders; and finally San Francisco, CA for meetings with San Francisco Sister Cities Board members;
- Creating SCI Youth, a new national brand for youth and launching its social networks global platforms such as Facebook, Twitter and Instagram for SCI Youth members to share its sister cities youth activities and unite global sister cities youth members into one platform;
- Bringing a major Japanese corporate sponsor to raise substantial funds;
- Bringing a famous Japanese music performer from Osaka, Japan to Aurora, CO for 2018 SCI Annual Conference;
- Serving as Southern California Sister Cities Board of Governors;
- Serving as Chairman of NextGen SubCommittee of Sister Cities International;
- Serving as co-chair of NextGen Track for 2018 SCI annual conference; and
- Participating as a keynote speaker for United Nations' NGO Global Partnership Summit and as a main panelist at the United Nations Headquarter in New York.
At the 2018 annual global conference, the total of over 500 sister cities members, speakers, supporters and youth leaders has gathered from throughout the United States and other nations to support and participate three-day sessions and its board elections. As the country representative for Japan and Eastern Asia, Koyamada gave his report of his sister cities activities on the main stage to hundreds of global audience during its annual conference.
Mayor of San Antonio Ron Nirenberg became the new Chairman of Sister Cities International.