I just received the following email from Apple:
On 12/1/2010, we received a notice from Nikoli.Co.Ltd. that Nikoli.Co.Ltd. believes your application named "Sudoku Grab" infringes Nikoli.Co.Ltd.'s intellectual property rights. In particular, Nikoli.Co.Ltd. believes you are infringing their trademark.
You can reach Nikoli.Co.Ltd. through Jimmy XXXX (phone: XXXXXX, email: XXXX). Please exchange correspondence directly with Nikoli.Co.Ltd..
We look forward to receiving written assurance that your application does not infringe Nikoli.Co.Ltd.'s rights, or that you are taking steps to promptly resolve the matter. Written assurance may include confirmation that your application does not infringe Nikoli.Co.Ltd.'s rights, an express authorization from Nikoli.Co.Ltd., or other evidence acceptable to Apple.
Under our terms of agreement, Apple may remove your application from the App Store at any time. You may remove your application using the steps provided below, for example, while you make any necessary changes to your application.
Based on this I have removed Sudoku Grab from sale in Japan.