In Medieval Europe there was an international mercenary industry. If a French ruler hired Genoese crossbowmen, or an Italian city state hired Swiss mercencaries, no one would even blink an eye. Transactions like that were perectly normal. The only rulers I've heard of who faced restrictions when hiring foreign mercenaries were the kings of England, and even they could hire as many as they wanted if they kept them outside of England, or they could hire English mercinaries for use at home.
But in Sengoku Japan, where were the Thai and Malay freelances, the Chinese and Korean companies, the Okinawan and Ainu spearmen and archers? AFAIK the only mercinaries used were Ashigaru, who were (I think) always Japanese.
As far as I know, East Asia did not develop an international mercenary industry. Malays, Chinese, Japanese, Koreans, Thai, etc. must have known about each other, but I've never heard of them forming free lance companies and serving abroad.
Any thoughts?