[Sangetsu]

You needn't. Bother learning much Japanese, unless you really want to learn it. Japanese do not hire foreigners for their Japanese ability, they hire people with skills which are hard to find in Japan.

The basic necessities required to live and work in Japan are a university education, and a skill which is in demand with Japanese employers. These skills are mainly foreign languages, finance, science, and engineering.

Manga artists and video game designers are not in high demand here lately, you would nest spend your time learning a real profession.