Japan is unique in that most every job, even fry guy at Mcdonalds, is covered by a Japanese person and not immigrants. The immigration laws are changing rapidly though in light of the growing demographic crisis-Japan seems hungry for foreigners right now. Below are the most frequent ways people stay employed in Sendai.
Most foreigners whether they are native English speakers or speak English as their second language are employed in some capacity as English teachers. The JET program is a popular avenue for mostly young and single adults to live in Japan. There are many school who will hire you both public and private.
Either of the above would classify you as a "highly skilled worker" and thus earn you a visa under that banner. Sendai generating a lot of momentum toward start-up companies and is attracting an ever larger population of computer specialist.
Japan legislature is considering extending the current six month Business Manager Visa to a full year. Within that time you will need to invest five million yen, take a lease on commercial office space and hire two local nationals. There is some flexibility, especially here in Tohoku where they are eager to help more foreigners to move here. Interestingly, once you establish your business you are eligible for several types of loans at incredibly low interest rates.