Kōji Yabe is a supporting character in Ace of Diamond Act II Second Season. He attends Inashiro Industrial High School, having entered the school after an invitation from Mei Narumiya. Yabe serves as a third baseman and pinch hitter, and wore jersey number 15 during the 89th National High School Baseball Championship. He is known for his skill at hitting inside pitches. Yabe is part of a team that tolerates Narumiya's cheeky personality, and he supports the team in a reserve or utility role. His background, motivations, and key relationships are defined by his connection to Narumiya and his place on the Inashiro Industrial roster, though specific details about his personal development are limited.