In general I prefer a native NT-manager. The guy must show more responsibility than somebody else, especially in such a *small* country like Japan. Most important thing is, than a NT accept inputs from other native managers as well, maybe even create a small team around him to have folks to help him who will scout and monitor players who are spread around the world. There are some countries and manager doing this, maybe it can help to add a little bit more quality to a NT. Carry the whole thing on one shoulder is okay if you have extensive online times. If not I guess it can be a burden ;)...
And as I mentionned before, all managers should put in 2 local heroes as trainees in there slots. That would be wonderful
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The method of learning Japanese recommended by experts is to be born as a Japanese baby and raised by a Japanese family, in Japan. And even then it is not easy...