Is it helpful to study abroad in Japan? If so what fields are good to pursue?

So with a degree in international affairs you can likely use it if you become a foreign service officer read diplomat. You can also convert it it to international buisness if you so choose and become a liaison to companies based elsewhere and go on the corpate track. Usually in your case you would work for either an American company in Japan or Japanese company in US or you can work for US in US or JP in JP it depends on preferences.

You can also go the political route by becoming a lobbyist for companies trying to influence policies such as Mitsubishi lobbyist asking us gov to lower tariffs etc.

Assuming you gain knowledge of Japanese it can be super helpful in any job especially on west coast.

You can also work with ngos in some fashion I’m not really sure how NGOs work you can also work for organizations such as UN that work with different countries on issues you can specify in environment buisness civil rights etc. And assuming you know Japanese and English there are lot of opportunities besides US-Japan jobs can include Japan-South Africa/India as most places have working knowledge of english