Japanese level, getting a PhD and landing a job as a University researcher

Hello everyone! My question is rather simple: Is it realistic to reach N1 and above from less than N5 (kana at best, no kanji nor grammar) while doing a PhD in english at a japanese university and then try to land a job as a University researcher? I know MEXT research scholarship offers some time to learn the language and prepare before enrolling into a University, however, I'm asking from a privately financed point of view. How difficult is it to reach that advanced level from virtually 0 at the same time as doing a PhD? Does inmersion benefits in that situation? Thank you so much for reading 🙂