Japan, of all the countries, has the most opportunities, units to take advantage of these opportunities, and time to attempt them. These moves might cost them some of their planes, but those are expendable(start with NINE!) to further expansion as well as most easily replaced due to their range and relative low cost.
By mentioning time, Japan is isolated enough to be able to recover if their opening round attacks go poorly.
J1 Buy = 2 tpt, inf = 17/17
2 inf (sz61) via sz61 tpt > brn *MT
CA,BB (sz61) > sz50 (dd, tpt)Philipines (2 inf)
inf (car) inf(oki) via sz51 tpt
2 inf (jap) via sz 62 tpt
3 inf, art (sz61) via sz61 tpts > bur (inf)
2 ftr (sz61) > sz35 (dd,tpt)
2 ftr (sz57) > sz56 (dd,tpt)
2 ftr (sz57), dd (sz51) > sz53 (BB)
However you want to attack China on the ground. This is not the strongest push, but also not the weakest.
3 inf (man), inf (kia) > Sui (inf)
2 inf (kia), ftr (jap) > fuk (inf)
3 inf (fic), ftr (for), ftr (man) > yun (inf,ftr)