One word of advice to all teachers in Japan who may plan on opening up their own school in the future:
Do Not Ever Tell Your Present Employer What Your Plans May or May Not Be!!
"That B will not give A any damage or loss after B leaves this school"
Is there also a Japanese version of the contract or is this the translation of the Japanese?
I do hope you didn't sign the contract yet goofy2feet.
I believe that since you already informed your employer that you may be leaving their school and might open up your own, that this is a kind of
"No compete" clause that is now inserted in your contract. In other words, if you quit, open up your own school in the same town and some of their students quit and start attending your school, it could be deemed as causing "damage" to your previous employers business and they can, and probably will, sue you. Even if a former student who previously quit their school, no longer attends at the present, and then starts attending your school in the future, it can be deemed as competing with them and that you are "stealing" their students thereby causing them "damage" and "loss".
The clause is ambiguous and is meant to be that way so that
any type of teaching you do in that town may be seen as causing "damage" and "loss" to their business and, BECAUSE it is in your contract and you signed it, thereby agreeing with it, they may just win in a court of Japanese law and you might just have to pay them damages. In other words, they may just have legally prevented you from ever teaching in that town again. The ambiguity will probably NOT play in your favor. You should have checked it out before you signed it and if you didn't sign it yet, get them to change it to be more specific or don't sign it.
How do I know this? Because the same thing happened to me back in the day when I foolishly informed my present employers that I had planned on opening up my own school. Luckily, for me my school was located in a different city many kilometers away because consultation with a lawyer proved that they could do it and that if I did teach in their city they could sue me as competing with them and causing damage and loss to them.
Good luck!