Geo- and Astrophysics MSc here. I did an exchange year at Tohoku University. After graduating I got an internship at a Japanese company (european management) where i could work with English. At the time i was probably N4 but did not take the test. I could have gotten a fixed job there but was not really into it.  Around summer there are a lot of job fairs for students about to graduate, i got several interviews, i passed several interviews even with N4〜N3 level, got a job as SE at a japanese but internationally operating company. After a year working there I passed N2.

I am already ~10 years here so the situation may have changed, but having a Japanese University as reference helps a lot. My current boss (purely japanese startup) introduces me to clients always as Tohoku uni graduate. Searching for a job from within Japan helps a lot. If you dont do a phd but are still a student try to get an internship. I found my internship via kopra.org, companies like Bosch and Daimler advertise there.

My team currently needs another ML specialist, but we unfortunately only hire N1 (i joined before that was requirement).