'Think Markets' are quite astute. Pepperstone for CFDs. However, some say that it is best to have a Japanese broker as they must keep to all the countries regulations and can sort out possible problems on the ground.
Both Japanese and Hong Kong markets think differently and HK has a lunch break. One of my shares in Hong Kong, 575, went wrong and it took my broker 26 months to put me in a position to trade the shares again - kept saying there was nothing they could do. Japanese shares are often highly priced and one share could cost as much as $2,000 - the reason many shares are only traded by Institutions. A Japanese broker may ask the equivalent of $50,000 to be held on an account with them. Some Japanese companies on the Mothers Market might have only 3,000 shares in issue and delivery can be tight.
Companies in Japan often merge causing foreigners difficulties.