As I had mentioned, Shimamoto had been the ace pitcher and cleanup hitter for Minoshima High School in Arida city in Wakayama Prefecture. I had also mentioned that he had led them to victory in the 1970 Spring Koshien Tournament but what I hadn't realized is that he pitched all 12 innings in the championship game against Hokuyo High School. This performance made him an "idol of Koshien" (according to his Japanese Wikipedia page) which I assume means he became extremely popular in a similar vein to Yuki Saitoh after the 2006 Summer tournament. Nankai took him with the first pick in the 1970 draft as a pitcher and briefly considered having him be a "two sword player" (he pitched in at least one exhibition game in the spring of 1971) before converting him to the outfield. He played sparingly in 1971, getting only eight at bats over seven games, so his election to the All Star team was purely based on his popularity from his high school days. He spent all of the next two seasons on Nankai's farm team and only played in nine games with the top team in 1974. He got his big break midway through the 1975 season when he was traded to the crosstown Kintetsu Buffaloes for Koichiro Sasaki. With the Buffaloes, he got a chance to play a little more regularly and while I don't think he ever really became a star he did make the All Star team two more times (1976 and 1977). He retired in 1985 and has been a baseball commentator on TV as well as head of a baseball school in Osaka since then.
Here's a card of him as a pitcher with Nankai from the 2007 BBM Draft Story set (#008):