Tenchu: Dark Secret (Tenchu: Dark Shadow in Japan) is a video game in the Tenchu series, developed by Polygon Magic and published by From Software for the Nintendo DS in 2006.
The game allows players to choose between Rikimaru and Ayame, two ninja assassins sent out to save a princess. There are more than 40 missions, as well as local wireless multiplayer combat and Wi-Fi capabilities which can be used to trade, buy and sell items around the world.
Source: Wikipedia, "Tenchu: Dark Secret", available under the CC-BY-SA License.