According to DC Watch, they published the camera sales rank in Japan in April, 2018. The Sony a7 III (Adorama, B&H, Amazon) is the best seller, sold far more better than second best camera Nikon D850 (B&H/Amazon/Adorama).
Below is the sales rank for April in Japan:
1st place: Sony α7 III
2nd: Nikon D850
3rd: Canon EOS Kiss X9
4th: Sony α7R III
5th: Nikon D3400
6th: Canon EOS 6D Mark II
7th: Canon EOS 5D Mark Ⅳ
8th: Olympus Tough TG-5
9th: Nikon D5600
10th: Sony Cyber-shot DSC-RX10M4