I'm Thai and I'll take luanguage course in Dalian, China for 4 months
then before back to Thailand I want to visit Japan for 1 weeks.
what should I do? because I ask Japanese embassy in Thailand and they told me
that I've to apply visa in China.

My dad will be my sponsor to guarantee all my expenditure in Japan during the visit.
Do my sponcer have to write any letter to guarantee?
(I'm 22 years old)
Thank you