In 1957, Tamotsu Kimura of the Nankai Hawks went 21-11 with a 2.47 ERA to win the Pacific League's Rookie Of The Year award. In 1958, he hurt his shoulder 12 innings into the season and never pitched again. He returned to the Hawks as an outfielder in 1960 and played for a couple more seasons, but he still hit like a pitcher.
Here's his 1958 Doyusha Team Name Back menko card, from when he was 23 and on top of the world:
Thanks to Japan Baseball Daily's Data Warehouse for the information on Kimura.