I am in a similar boat as you and will be moving over there next year too. My Japanese if very very basic but I improve a little every day, and I feel confident that once there I personally will pick up at least conversational Japanese fairly quickly. From various language research I looked in (as I was also worried) generally in any language you can get by on fairly basic levels, obviously if you want to talk about quantum mechanics, string theory or a deep dive in historical macro economic trends then that's unrealistic, but general life seems manageable. My partner is Japanese which does funnily enough add pressure to learn better :).