An Xbox 360 MMO is the number one game in Japan, where Microsoft's console generally struggles.
The game is Capcom's Monster Hunter Frontier Online, which sold 93,000 units for the week ending 27th June.
It beat Konami's DS title Love Plus +, Atelier Totori: Alchemist of Arland 2 from Gust, and Konami's Tokimeki Memorial: Girl's Side 3rd Story.
Monster Hunter Frontier Online - a port of the original 2007 PC game - comes with a free 12-month Xbox Live Gold membership and a code for 30 days of online play. Continue playing after that point and you'll have to pay around £10 a month.
The Monster Hunter franchise is huge in Japan, so it comes as no surprise to see Frontier Online do well there. But the series has traditionally enjoyed success on Sony's PlayStation Portable, which allows fans to hunt those monsters on the move.
There's still no word on a Western release.