Koki Kitayama (26), pitcher for the Nippon Nippon-Ham 's representative for the WBC, joined the team's voluntary training in Nago, Okinawa, on the 28th and entered bullpen. He threw nine pitches using the WBC ball. Regarding his first selection to the big stage, Kitayama reflected on the weight of the Japanese flag, saying, "Before the game, the national anthem is played, and at that moment, I really feel that it's thanks to all the people who have helped me up until now that we're able to baseball peacefully and be able to stand on this stage. Taking into account the past background, it's meaningful to turn the strength of the people who support me now into my own power. I want to be a source of energy and inspiration to people all over Japan."

During the off-season, he attended the same training facility in Osaka as Dodgers pitcher Yamamoto, and was also taught by trainer Osamu Yada, whom Yamamoto has immense confidence in. He also trained with Yamamoto, who is a year older than him, and said, "Being teammates together, I think I'll learn something new, and I think there will be a lot more to feel than just learning with my head, so I'm really excited that it will ignite a fire in my heart." He looked forward to working together with his "fellow alumnus."