I went to probably the largest Hello Work in Tokyo -- and while I speak decent enough Japanese, for sensitive/legal topics, I prefer English. Anyway, they only had 1 staff in the entire building that can speak English -- yes, just one person. Also, all signage and documentation is in Japanese.

So bring a friend to translate if you can.

Also, in order to claim your benefits, you need to prove that you are actively seeking a job. You'll have to attend an hour long orientation (in Japanese) -- not so bad. Then after you have to regularly visit their office to look for jobs. I couldn't be arsed...

Also, about your job -- don't do it. If you are already planning on leaving, have them pay you out. And keep in mind: if you quit, you forfeit a large portion of your unemployment insurance.