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

Taichi Tokonatsu is a young baseball player. With amazing batting and pitching skills, Taichi was the main star during the National High School Baseball Championship. Loved by baseball fans all over Japan, he is guaranteed to become a great professional baseball player. Unfortunately, this future would never be achieved after he dies in an accident during his return from the tournament. Following his passing, Taichi meets with God, who reveals that he can return him to Earth. However, he imposes a condition: Taichi must first go to Galia, a world where all international conflicts are resolved through baseball. Furthermore, he is tasked with helping Freedom, Galia's weakest nation representing the human race. Accepting God's proposal, Taichi wakes up in this new world only to discover that the majority of the population has been enslaved by other nations—leaving Freedom's baseball team with only women, children, and the elderly. With Freedom on the brink of being erased from the map, Taichi must utilize everything he knows about the sport to save the most vulnerable race in Galia. [Written by MAL Rewrite]