Origins of Team Names

Taken from "You Gotta Have Wa" by Robert Whiting, Chapter 2:

Shoriki [owner of Yomiuri Shimbun] was unfazed [by the stabbing by a rightist for his sponsoring the MLB All Star Tour in 1934]. Encouraged by the response of the fans to Ruth, he established Japan's first professional baseball team, the Dai Nippon Tokyo Yakyu Kurabu (the Great Japan Tokyo Baseball Club), in December 1934, quickly signing up Sawamura and other top Japanese stars.

Dai Nippon toured the U.S. in 1935, playing 102 various PCL and semipro teams and winning 93 games. Wearing uniforms with numbers written in Chinese characters, they confused Americans trying to keep score. Their lengthy name was also so difficult for their hosts to master that Shoriki changed it to the Tokyo Giants, after the National League team from New York.

Six other teams joined the Tokyo Kyojin (Japanese for Giants) and formed Japan's first professional baseball league in 1936. The other six teams were the Hanshin Tigers, Nagoya, Dai-Tokyo, Nagoya Kinsachihiko (Goldfish?), Tokyo Senators, and Hankyu. (As you can see, not all teams had mascots their first year.)

Yomiuri changed the name of the team to Yomiuri Giants in 1947, and that has been their name ever since. While their uniforms have had the word "Tokyo" on them often since 1947, it has not been part of their official name. Furthermore, newspapers still print the Giants' name as "Kyojin" in the standings. I think that this is because none of the other newspapers want to print "Yomiuri," their main competition - but that doesn't explain why Yomiuri does this in their own papers, too.

Sources:
"You Gotta Have Wa," Robert Whiting, ISBN 0-679-72947-X
"2003 Baseball Record Book," Baseball Magazine Sha, ISBN 4-583-03724-4

Lefty O'Doul of the New York Giants, who was very close Shioriki Matsutaro, suggested the name since Giants represented New York, which was similar to Tokyo. Then Tigers were named since Osaka was similar to Detroit which was an industrial city.