Thank you for your reply, everyone!
All you have a lot of knowledge!!
Dear granderbox
You have wrotten all what I would like to say!
As you said, I will play minor and major combination depending on tunes.
Now I try to play "La hulotte/la m�re est blanche" recorded by Patric Bouffard(Rabaterie).
The first tune is G minor to G, and second tune is G.
I play it on G/C/Acc, easily bass and treble.
Dear EeeJay
Yea, you mean full size acorrdeons are played in France.
Almost all Japanease don't have well-built physique(I am 170 cm hight).
I manage to play Castagnari Mory, but it is slightly large for me.
I think it is also useful the C#/D/G system!
I am temped by the box EeeJay shown.
I have ordered many instruments eg B. Gaillard, Maugein C/F/Acc 3 voice, cornemuse etal.
My wife is very strict...