[Sangetsu]

You are mistaken about the full time work requirement. Pretty much any Japanese employer will limit you to a part-time 29.5 hour work week (which somehow magically becomes at least 40 hours).

On the other hand, employers usually hire people on an annual basis, having you sign a one-year contract. Most employers will not go to the trouble of hiring, sponsoring, and training a person who will only stay for 6 months. Those who hire teachers to work for shorter terms usually want those teachers to already have experience and a work visa.

Your best bet is to get hired, sign a one year contract, and leave after 6 months. Many people get hired, sign the contract, get the visa, and leave immediately to do something else.