Yakyuu de Sensou suru Isekai de Chou Koukou-kyuu Ace ga Jakushou Kokka wo Sukuu you desu.  

Yakyuu de Sensou suru Isekai de Choukoukoukyuu Ace ga Jakushou Kokka wo Sukuu Youdesu, 야구가 전쟁인 이세계에서 탈고교급 에이스가 약소국가를 구한다

In Japan, there was a talented high school student named Taichi Tokonatsu who excelled in both batting and pitching during the National High School Baseball Championship. He gained widespread popularity among fans throughout the country and was predicted to become a successful professional ballplayer in the future. However, his dream was cut short when he met with an accident on his way back from the tournament. After his passing, he met with God who offered him the chance to return to Earth with one condition-he must first visit Galia, a world where international conflicts are resolved through baseball. Additionally, he was tasked with helping Freedom, Galia's weakest nation representing humanity. Although initially hesitant, Taichi agreed to God's proposal and woke up in this new world only to find that most of its population had been enslaved by other nations. This left Freedom's baseball team with only women, children, and elderly members. In order to save this vulnerable race in Galia, Taichi utilized his extensive knowledge of baseball to help Freedom team win against their oppressors.